CA3141850A1 - Highly efficient acid-distributing method considering spatio-temporal distribution characteristics of acid corrosion crack conductivity - Google Patents
Highly efficient acid-distributing method considering spatio-temporal distribution characteristics of acid corrosion crack conductivityInfo
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- CA3141850A1 CA3141850A1 CA3141850A CA3141850A CA3141850A1 CA 3141850 A1 CA3141850 A1 CA 3141850A1 CA 3141850 A CA3141850 A CA 3141850A CA 3141850 A CA3141850 A CA 3141850A CA 3141850 A1 CA3141850 A1 CA 3141850A1
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- acid
- gel
- stage
- crack
- fracturing
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- E—FIXED CONSTRUCTIONS
- E21—EARTH DRILLING; MINING
- E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
- E21B43/25—Methods for stimulating production
- E21B43/26—Methods for stimulating production by forming crevices or fractures
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH DRILLING; MINING
- E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B33/00—Sealing or packing boreholes or wells
- E21B33/10—Sealing or packing boreholes or wells in the borehole
- E21B33/13—Methods or devices for cementing, for plugging holes, crevices, or the like
Abstract
Provided is a highly efficient acid-distributing method considering spatio- temporal distribution characteristics of acid corrosion crack conductivity. The method comprises: (1) judging the conditions for acid fracturing construction are met, based on seismic data and drilling data in blocks; (2) controlling crack height by adopting an artificial gel barrier technology; (3) carrying out the acid fracturing construction, pumping preflush fluid to press out the cracks, pumping the acid-liquid commination to etch the crack wall and press out new cracks; (4) adopting a three-stage process temporarily hindering acidization, injecting temporary plugging fluid to effectively plug the high-permeability area, followed by injecting gel acid to regain the acid corrosion conductivity of the high-permeability area; (5) at the production stage of oil- gas wells, injecting an acid-liquid combination at a pressure slightly higher than that to open the cracks when the formation pressure drops to 70% of the original formation pressure.
Description
HIGHLY EFFICIENT ACID-DISTRIBUTING METHOD CONSIDERING SPATIO-TEMPORAL DISTRIBUTION CHARACTERISTICS OF ACID CORROSION
CRACK CONDUCTIVITY
TECHNICAL FIELD OF THE INVENTION
The invention belongs to the field of oil-gas field development, and specifically relates to a highly efficient acid-distributing method considering spatio-temporal distribution characteristics of acid corrosion crack conductivity.
DESCRIPTION OF THE PRIOR ART
In recent years, domestic researchers have attached great importance to exploring an unconventional reservoir stratum such as high-temperature deep carbonate rocks, and industry participants have laid great stress on improving the exploitation efficiency of unconventional oil-gas resources and the recovery efficiency of a reservoir stratum for a long time. Acid fracturing is one of the important methods used in the petroleum industry so as to increase the single well production and the recovery efficiency of an oil-gas reservoir, and it greatly contributes to increasing the production and tapping the potentials for the old oil-gas fields and exploring and developing new oil-gas fields. Among them, the acid corrosion crack conductivity is an important factor that determines the construction effect.
At present, there are many methods to improve the acid corrosion crack conductivity. Some adopt a means of injecting acid with variable viscosity and displaced volume, which forms uneven etching while increasing the penetration distance of cracks, and even an independent means of injecting acid is adopted for acid liquor with different viscosity so as to uniformly distribute the acid and optimize the effect of acid fracturing. Some adopt a process of multistagedly and alternately injecting acid, which raises the length of acid corrosion cracks and the density of remote cracks by setting appropriate process parameters, as well as increases the probability of leading to the reservoir strata around the well.
There are still some methods to repeat acid fracturing combined with a specific process for the construction effect after one acid fracturing, which optimize the conductivity and stabilization time of acid corrosion cracks, while increasing the distance of cracks' extension and leading to the reservoir strata on both sides of manmade cracks. However, in these acid-distributing methods, although considering the structural parameters of manmade cracks, the distribution of crack networks in a reservoir, and the influence of permeability damage of acid corrosion cracks on the acid corrosion conductivity, they failed to effectively extend the development and production cycle for oil-gas fields, and limited the degree of reservoir development.
Therefore, the invention proposes a highly efficient acid-distributing method considering spatio-temporal distribution characteristics of acid corrosion crack conductivity, which is of great significance for achieving high-efficiency, low-cost and stable development of oil-gas reservoirs.
SUMMARY OF THE INVENTION
The objectives of the invention are to provide a highly efficient acid-distributing method considering spatio-temporal distribution characteristics of acid corrosion crack conductivity, which optimizes the acid Date Recue/Date Received 2021-09-24 corrosion crack conductivity based on expansion to the boundary that the acid fracturing spreads to , and improves the effect of supplying diversion networks with oil-gas for a long time. The method can effectively improve the degree of developing a reservoir stratum, overcome the shortcomings and deficiencies of the prior arts, and have broad market application prospects.
In order to achieve the above technical objectives, the invention adopts the following technical solutions.
A highly efficient acid-distributing method considering spatio-temporal distribution characteristics of acid corrosion crack conductivity sequentially includes the following steps:
Si. analyzing the structural feature, lithological characteristics, porosity type, physical characteristics and pressure-temperature characteristics of a carbonate reservoir stratum, based on seismic data and drilling data in blocks, so as to determine whether the following conditions exist:
a. the reservoir stratum being adjacent to the aquifer;
b. the crack expansion during the fracturing process being easy to cause the through-strata phenomenon, with small barrier stress difference between barriers;
c. the reservoir stratum having strong heterogeneity;
taking the measure to control crack height according to S2 if they exist but do not meet the conditions for acid fracturing construction, carrying out the acid fracturing construction according to S3 if they do not exist and meet the conditions for acid fracturing construction.
S2. taking the measure to control crack height that includes the following processes:
adopting artificial gel barrier technology controlling crack height to the target layer, injecting water-based fracturing fluid into a stratum with carrying the gel particles, which are cemented with each other to form a gel barrier, thereby blunting the crack tip and increasing the resistance value of the upper and lower ends of the crack, further controlling the extension of crack height so as to provide the requirement to optimize the width and penetration distance of the acid corrosion crack(Peng Yu. research on high-tech technology and model of acid fracturing controlling cracks [DJ. Southwest Petroleum University, 2014).
In the measure to control crack height adopted by the invention, the pumped displaced volume is generally selected to be set at 3-7m3/min, similar to artificial barrier technology for sandstone reservoirs.
Under construction with the same addition amount, the toughness provided by the gel barrier when resisting extension of the crack height is more than 5 times the toughness provided by the conventional artificial barrier, so under precondition of effectively controlling the crack height, the addition amount of gels is set to 20% of that of ceramcite. The optimal addition amount of ceramcite can be deduced from the theoretical model based on the crack extension criterion, and then determined by Newton Algorithm (Yi Xiangyi, Wang Daobing, Hou Yanhong, Zhou Fujian, Liu Xiongfei, Li Xiuhui. a method for determining the optimal addition amount of artificial barrier agent for controlling fracture height[Jj.Journal of Oil and Gas Technology,2012, 34(06):145-147+ 170). At the same time, in order to reduce the influence of acid-rock reaction on the temperature field where the gel particles are situated in the later acid fracturing stage, the mineralization range of the water-based fracturing fluid is set to be 0-100g/L, according to the characteristic that the solidification time of the gel barrier increases with an increase in the mineralization, during the construction process, the deposition and cementation time of gels are controlled by adjusting mineralization, thereby getting the formation of the gel barrier under control.
CRACK CONDUCTIVITY
TECHNICAL FIELD OF THE INVENTION
The invention belongs to the field of oil-gas field development, and specifically relates to a highly efficient acid-distributing method considering spatio-temporal distribution characteristics of acid corrosion crack conductivity.
DESCRIPTION OF THE PRIOR ART
In recent years, domestic researchers have attached great importance to exploring an unconventional reservoir stratum such as high-temperature deep carbonate rocks, and industry participants have laid great stress on improving the exploitation efficiency of unconventional oil-gas resources and the recovery efficiency of a reservoir stratum for a long time. Acid fracturing is one of the important methods used in the petroleum industry so as to increase the single well production and the recovery efficiency of an oil-gas reservoir, and it greatly contributes to increasing the production and tapping the potentials for the old oil-gas fields and exploring and developing new oil-gas fields. Among them, the acid corrosion crack conductivity is an important factor that determines the construction effect.
At present, there are many methods to improve the acid corrosion crack conductivity. Some adopt a means of injecting acid with variable viscosity and displaced volume, which forms uneven etching while increasing the penetration distance of cracks, and even an independent means of injecting acid is adopted for acid liquor with different viscosity so as to uniformly distribute the acid and optimize the effect of acid fracturing. Some adopt a process of multistagedly and alternately injecting acid, which raises the length of acid corrosion cracks and the density of remote cracks by setting appropriate process parameters, as well as increases the probability of leading to the reservoir strata around the well.
There are still some methods to repeat acid fracturing combined with a specific process for the construction effect after one acid fracturing, which optimize the conductivity and stabilization time of acid corrosion cracks, while increasing the distance of cracks' extension and leading to the reservoir strata on both sides of manmade cracks. However, in these acid-distributing methods, although considering the structural parameters of manmade cracks, the distribution of crack networks in a reservoir, and the influence of permeability damage of acid corrosion cracks on the acid corrosion conductivity, they failed to effectively extend the development and production cycle for oil-gas fields, and limited the degree of reservoir development.
Therefore, the invention proposes a highly efficient acid-distributing method considering spatio-temporal distribution characteristics of acid corrosion crack conductivity, which is of great significance for achieving high-efficiency, low-cost and stable development of oil-gas reservoirs.
SUMMARY OF THE INVENTION
The objectives of the invention are to provide a highly efficient acid-distributing method considering spatio-temporal distribution characteristics of acid corrosion crack conductivity, which optimizes the acid Date Recue/Date Received 2021-09-24 corrosion crack conductivity based on expansion to the boundary that the acid fracturing spreads to , and improves the effect of supplying diversion networks with oil-gas for a long time. The method can effectively improve the degree of developing a reservoir stratum, overcome the shortcomings and deficiencies of the prior arts, and have broad market application prospects.
In order to achieve the above technical objectives, the invention adopts the following technical solutions.
A highly efficient acid-distributing method considering spatio-temporal distribution characteristics of acid corrosion crack conductivity sequentially includes the following steps:
Si. analyzing the structural feature, lithological characteristics, porosity type, physical characteristics and pressure-temperature characteristics of a carbonate reservoir stratum, based on seismic data and drilling data in blocks, so as to determine whether the following conditions exist:
a. the reservoir stratum being adjacent to the aquifer;
b. the crack expansion during the fracturing process being easy to cause the through-strata phenomenon, with small barrier stress difference between barriers;
c. the reservoir stratum having strong heterogeneity;
taking the measure to control crack height according to S2 if they exist but do not meet the conditions for acid fracturing construction, carrying out the acid fracturing construction according to S3 if they do not exist and meet the conditions for acid fracturing construction.
S2. taking the measure to control crack height that includes the following processes:
adopting artificial gel barrier technology controlling crack height to the target layer, injecting water-based fracturing fluid into a stratum with carrying the gel particles, which are cemented with each other to form a gel barrier, thereby blunting the crack tip and increasing the resistance value of the upper and lower ends of the crack, further controlling the extension of crack height so as to provide the requirement to optimize the width and penetration distance of the acid corrosion crack(Peng Yu. research on high-tech technology and model of acid fracturing controlling cracks [DJ. Southwest Petroleum University, 2014).
In the measure to control crack height adopted by the invention, the pumped displaced volume is generally selected to be set at 3-7m3/min, similar to artificial barrier technology for sandstone reservoirs.
Under construction with the same addition amount, the toughness provided by the gel barrier when resisting extension of the crack height is more than 5 times the toughness provided by the conventional artificial barrier, so under precondition of effectively controlling the crack height, the addition amount of gels is set to 20% of that of ceramcite. The optimal addition amount of ceramcite can be deduced from the theoretical model based on the crack extension criterion, and then determined by Newton Algorithm (Yi Xiangyi, Wang Daobing, Hou Yanhong, Zhou Fujian, Liu Xiongfei, Li Xiuhui. a method for determining the optimal addition amount of artificial barrier agent for controlling fracture height[Jj.Journal of Oil and Gas Technology,2012, 34(06):145-147+ 170). At the same time, in order to reduce the influence of acid-rock reaction on the temperature field where the gel particles are situated in the later acid fracturing stage, the mineralization range of the water-based fracturing fluid is set to be 0-100g/L, according to the characteristic that the solidification time of the gel barrier increases with an increase in the mineralization, during the construction process, the deposition and cementation time of gels are controlled by adjusting mineralization, thereby getting the formation of the gel barrier under control.
2 Date Recue/Date Received 2021-09-24 S3. carrying out the acid fracturing construction, by means of pumping with isochronous five-stage deceasing displaced volume, which includes the following processes:
Stage 1: pumping preflush fluid to press out the cracks and decreasing the formation temperature, wherein the pumped displaced volume at this stage is equal to the displaced volume of the conventional acid fracturing;
Stage 2: pumping gel acid, etching the crack wall more evenly and improving the crack conductivity with use of the characteristics that 11+ is slowly released, wherein the pumped displaced volume at this stage is 80% of the displaced volume of the conventional acid fracturing;
Stage 3: firstly pumping gel acid to supplement the II+ concentration in the crack, and then pumping non-reactive fluid so as to push the acid to etch the crack wall at the far end of a well, wherein the usage ratio of the gel acid and the non-reactive fluid at this stage is 4:1, and the pumped displaced volume at this stage is 60% of the displaced volume of the conventional acid fracturing;
Stage 4: using a combination of the gel acid and the non-reactive fluid, as the same as the pumping procedure in Stage 3, wherein the usage ratio of both liquid is 4:1, and the pumped displaced volume at this stage is 40% of the displaced volume of the conventional acid fracturing;
Stage 5: pumping conventional acid, definitely improving the conductivity of the crack near the well end with use of the characteristics that the acid-rock reaction is faster in speed, wherein the pumped displaced volume at this stage is 20% of the displaced volume of the conventional acid fracturing.
Where, the displaced volume of the conventional acid fracturing is 4-16m3/min, and the displaced volume of pumping an acid-liquid combination is calculated based on this. The preflush fluid system is hydroxypropyl guar gum (0.5%) + fungicide + clay stabilizer + demulsifier + pH
regulator (Cai Daqing, Zhou Hao. acid fracturing technology applied into carbonate reservoirs in Tahe Oilfield[Jj. Drilling and Production Technology, 2004(03):44-46+62+3). The gel acid system is HC1 (20%) + gel agent (0.8%) +
corrosion inhibitor (4%)+ demulsification and cleanup additive (2%)+ iron ion stabilizer (2%) (Xu Xingjuan, Fu Yueyong, Yang Jinling, Jia Hongzhan, Wang Yunyun, Cui Fuyuan, Li Wenjie, Yang Bin.
research and field application of gel acid system for acidization at 180 C[I1Petrochemical Industry Application, 2018,37(07) :11-15). The non-reactive fluid is conventional water-based fracturing fluid or formation water. The conventional acid is HC1(20%)+KMS-6 (2.0%)+BD1-2 (1%) +BD1-3 (1%) + BD1-5 (1%) (Li Nianyin. Evaluation of acid fracturing effect of high temperature deep well in fractured oil-gas reservoirs in Tarim lunan buried hill [DJ. Southwest Petroleum University, 2006). The total liquid volume of acid fracturing construction is 300-500m3, which is determined in combination with the crack length to be fractured and the maximum value allowable to ground equipment. The usage amount of preflush fluid is 33% of the total liquid volume, the usage amount of the gel acid is 53% of the total liquid volume, and the usage amount of the water-based fracturing fluid or the formation water is 7%
of the acid-liquid combination. The usage amount of the conventional acid is 7% of the total liquid volume.
S4. after fracturing and acidizing, in order to prevent the low-permeability layer from getting effective modification, adopting the construction temporarily hindering acidization after completing the acid injection, thereby optimizing the spatial distribution characteristics of the acid corrosion crack conductivity, simultaneously, omitting the acidization operation to unblock before the construction temporarily hindering acidization, and reducing the amount of acid fluid and construction time.
Considering the on-site
Stage 1: pumping preflush fluid to press out the cracks and decreasing the formation temperature, wherein the pumped displaced volume at this stage is equal to the displaced volume of the conventional acid fracturing;
Stage 2: pumping gel acid, etching the crack wall more evenly and improving the crack conductivity with use of the characteristics that 11+ is slowly released, wherein the pumped displaced volume at this stage is 80% of the displaced volume of the conventional acid fracturing;
Stage 3: firstly pumping gel acid to supplement the II+ concentration in the crack, and then pumping non-reactive fluid so as to push the acid to etch the crack wall at the far end of a well, wherein the usage ratio of the gel acid and the non-reactive fluid at this stage is 4:1, and the pumped displaced volume at this stage is 60% of the displaced volume of the conventional acid fracturing;
Stage 4: using a combination of the gel acid and the non-reactive fluid, as the same as the pumping procedure in Stage 3, wherein the usage ratio of both liquid is 4:1, and the pumped displaced volume at this stage is 40% of the displaced volume of the conventional acid fracturing;
Stage 5: pumping conventional acid, definitely improving the conductivity of the crack near the well end with use of the characteristics that the acid-rock reaction is faster in speed, wherein the pumped displaced volume at this stage is 20% of the displaced volume of the conventional acid fracturing.
Where, the displaced volume of the conventional acid fracturing is 4-16m3/min, and the displaced volume of pumping an acid-liquid combination is calculated based on this. The preflush fluid system is hydroxypropyl guar gum (0.5%) + fungicide + clay stabilizer + demulsifier + pH
regulator (Cai Daqing, Zhou Hao. acid fracturing technology applied into carbonate reservoirs in Tahe Oilfield[Jj. Drilling and Production Technology, 2004(03):44-46+62+3). The gel acid system is HC1 (20%) + gel agent (0.8%) +
corrosion inhibitor (4%)+ demulsification and cleanup additive (2%)+ iron ion stabilizer (2%) (Xu Xingjuan, Fu Yueyong, Yang Jinling, Jia Hongzhan, Wang Yunyun, Cui Fuyuan, Li Wenjie, Yang Bin.
research and field application of gel acid system for acidization at 180 C[I1Petrochemical Industry Application, 2018,37(07) :11-15). The non-reactive fluid is conventional water-based fracturing fluid or formation water. The conventional acid is HC1(20%)+KMS-6 (2.0%)+BD1-2 (1%) +BD1-3 (1%) + BD1-5 (1%) (Li Nianyin. Evaluation of acid fracturing effect of high temperature deep well in fractured oil-gas reservoirs in Tarim lunan buried hill [DJ. Southwest Petroleum University, 2006). The total liquid volume of acid fracturing construction is 300-500m3, which is determined in combination with the crack length to be fractured and the maximum value allowable to ground equipment. The usage amount of preflush fluid is 33% of the total liquid volume, the usage amount of the gel acid is 53% of the total liquid volume, and the usage amount of the water-based fracturing fluid or the formation water is 7%
of the acid-liquid combination. The usage amount of the conventional acid is 7% of the total liquid volume.
S4. after fracturing and acidizing, in order to prevent the low-permeability layer from getting effective modification, adopting the construction temporarily hindering acidization after completing the acid injection, thereby optimizing the spatial distribution characteristics of the acid corrosion crack conductivity, simultaneously, omitting the acidization operation to unblock before the construction temporarily hindering acidization, and reducing the amount of acid fluid and construction time.
Considering the on-site
3 Date Recue/Date Received 2021-09-24 construction cost and the effectiveness of the construction temporarily hindering acidization, the present adopts a three-stage process temporarily hindering acidization. The pumping procedures in each stage of the process temporarily hindering acidization are the same, that is, a certain amount of temporary plugging fluid is injected to effectively plug the high-permeability area and increase the acid intake in the low-permeability area during the subsequent acidization process. Cellulose (6mm) is used as temporary plugging material in the temporary plugging fluid, then gel acid is injected to fully dissolve the cellulose in the stratum and regain the acid corrosion conductivity of the high-permeability area.
Where, the gel acid is HC1 (10%) + gel agent (0.8%) + corrosion inhibitor (4%) + demulsification and cleanup additive (2%) + iron ion stabilizer (2%). Cellulose (6mm) is used as temporary plugging material in the temporary plugging fluid, in which the fiber concentration is 1%-2%, and the cellulose can be completely degraded when the 11+ concentration and temperature are high. The displaced volume of temporary plugging liquid is 1-3m3/min, the displaced volume of acid fluid is 2-7m3/min, and the strength of cellulose is 1.5-2.5kg/m. The specific value of cellulose consumption is determined in combination with the length of the horizontal section and the maximum value allowable to ground equipment. The acid injection time after temporary plugging at each stage is roughly equivalent to the fiber dissolution time, so the usage amount of the acid fluid is calculated based on this, and temporary plugging at next stage will be performed immediately after completing the acid injection. In addition, in order to lower the ambient temperature and isolate the acid fluid from the fibers, high-viscosity fracturing fluid in sections is injected at beginning and ending of the temporary plugging fluid, respectively, and the usage amount for each injection is 50% of the temporary plugging fluid.
S5. At the production stage of oil-gas wells, because the gradual decrease of formation pressure and the increase of crack closure pressure make the acid corrosion crack conductivity gradually decrease with the production time, resulting in a decline in the productivity of the oil-gas wells, slowly injecting a small amount of acid into the reservoir with low displaced volume to clean the well when the formation pressure drops to 70% of the original formation pressure, after cleaning the well, injecting an acid-liquid combination at the pressure slightly higher than that to open the cracks, by monitoring a large number of indoor simulation tests and on-site production data. The acid-liquid combination flows in the closed cracks and dissolves the walls of the cracks to form grooves, which optimizes the distribution of the acid corrosion conductivity affected by the production time, and regains the crack conductivity to more than 84% of the initial conductivity after closed acidization construction. The acid-liquid combination is self-generating acid + gel acid + hydrochloric acid, and the usage amount of the three acids is 40%, 35% and 25% of the total amount of the acid-liquid combination, respectively. The three acids are sorted into the self-generating acid, the gel acid and the hydrochloric acid according to the acid-rock reaction time from high to low.
Therefore, injecting into the stratum in this order can effectively improve the conductivity of the far-end, middle part and near-end of the cracks.
Where, the self-generating acid is synthesized by reacting a carbonyl compound having high polymerization degree and a chlorine-containing organic ammonium salt by 1:1 (Wang Yang, Yuan Qingyun, Li Li. deep penetration and acid fracturing technology for self-generating acid in carbonate reservoirs in Tahe OilfieldO.Petroleum Drilling Technology,2016,44(05):90-93). The gel acid is the same as S3. The mass concentration of the hydrochloric acid is 20%. The displaced volume of injecting the acid-liquid
Where, the gel acid is HC1 (10%) + gel agent (0.8%) + corrosion inhibitor (4%) + demulsification and cleanup additive (2%) + iron ion stabilizer (2%). Cellulose (6mm) is used as temporary plugging material in the temporary plugging fluid, in which the fiber concentration is 1%-2%, and the cellulose can be completely degraded when the 11+ concentration and temperature are high. The displaced volume of temporary plugging liquid is 1-3m3/min, the displaced volume of acid fluid is 2-7m3/min, and the strength of cellulose is 1.5-2.5kg/m. The specific value of cellulose consumption is determined in combination with the length of the horizontal section and the maximum value allowable to ground equipment. The acid injection time after temporary plugging at each stage is roughly equivalent to the fiber dissolution time, so the usage amount of the acid fluid is calculated based on this, and temporary plugging at next stage will be performed immediately after completing the acid injection. In addition, in order to lower the ambient temperature and isolate the acid fluid from the fibers, high-viscosity fracturing fluid in sections is injected at beginning and ending of the temporary plugging fluid, respectively, and the usage amount for each injection is 50% of the temporary plugging fluid.
S5. At the production stage of oil-gas wells, because the gradual decrease of formation pressure and the increase of crack closure pressure make the acid corrosion crack conductivity gradually decrease with the production time, resulting in a decline in the productivity of the oil-gas wells, slowly injecting a small amount of acid into the reservoir with low displaced volume to clean the well when the formation pressure drops to 70% of the original formation pressure, after cleaning the well, injecting an acid-liquid combination at the pressure slightly higher than that to open the cracks, by monitoring a large number of indoor simulation tests and on-site production data. The acid-liquid combination flows in the closed cracks and dissolves the walls of the cracks to form grooves, which optimizes the distribution of the acid corrosion conductivity affected by the production time, and regains the crack conductivity to more than 84% of the initial conductivity after closed acidization construction. The acid-liquid combination is self-generating acid + gel acid + hydrochloric acid, and the usage amount of the three acids is 40%, 35% and 25% of the total amount of the acid-liquid combination, respectively. The three acids are sorted into the self-generating acid, the gel acid and the hydrochloric acid according to the acid-rock reaction time from high to low.
Therefore, injecting into the stratum in this order can effectively improve the conductivity of the far-end, middle part and near-end of the cracks.
Where, the self-generating acid is synthesized by reacting a carbonyl compound having high polymerization degree and a chlorine-containing organic ammonium salt by 1:1 (Wang Yang, Yuan Qingyun, Li Li. deep penetration and acid fracturing technology for self-generating acid in carbonate reservoirs in Tahe OilfieldO.Petroleum Drilling Technology,2016,44(05):90-93). The gel acid is the same as S3. The mass concentration of the hydrochloric acid is 20%. The displaced volume of injecting the acid-liquid
4 Date Recue/Date Received 2021-09-24 combination is 1-4m3/min, and the total usage amount of the acid-liquid combination is 25% of the usage amount of the acid with the same type and concentration under conventional acid fracturing technology.
The acid used for cleaning wells is hydrochloric acid with a mass concentration of 10%, the displaced volume is 1.1-2.3m3/min, and the usage amount is 10-15% of the total amount of the acid-liquid combination.
Compared with the prior art, the invention has the following beneficial effects:
The invention has the characteristics such as high acid-liquid utilization efficiency, strong acid fracturing timeliness, long effective stable production time, and remarkable production-increasing effect, and is conducive to the stable and efficient development of high-temperature deep carbonate reservoirs.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG.1 shows the acid fracturing production curve of Well X.
FIG.2 is a schematic diagram of the effective closed pressure distribution in the acid corrosion cracks of Well Y when the stratum stress drops to 70%.
FIG.3 shows the influence of the effective closed stress of Well Y on the acid corrosion conductivity.
FIG.4 is a schematic diagram of the effective closed pressure distribution in the acid corrosion fractures after closure acidization of Well Y
FIG.5 shows the acid fracturing production curve of Well Y.
DETAILED DESCRIPTION OF THE INVENTION
The invention will be further described below based on the drawings and examples to help to understand it for a person skilled in the art. However, a person skilled in the art should note that the scope of the invention is not limited to specific implementation methods, as long as changes encountered are define by the appended claims and within the scope of the spirit and scope of the invention, they are all claimed by the invention.
Example 1 The reservoir in the well region where Well X is located has good homogeneity, with a thickness of 25-28m, but the water near the reservoir gathers and the barrier stress is low. In order to avoid leading to the lower water during the acid fracturing process on the basis of leading to the oil-gas storage space at the far-end of the well, the water-based fracturing fluid used to carry gel particles with a density slightly higher than that of the fracturing fluid is injected into the stratum, and the mineralization is controlled to 80g/L
during the injection process to ensure that the gel does not prematurely coagulate. After the gel particles reach the target position, the mineralization is adjusted to 10g/L, promoting the gel particles to absorb water and swell so as to form a high-strength gel barrier and increase the threshold of the stress through strata. The volume of the water-based guar gum fracturing fluid used in this process is 312.6m3, the volume of the gel particles is 7.6m3, and the displaced volume is 4.5m3/min. The construction scale, the liquid ratio and the displaced volume in construction are optimized for parameters to further improve the spatial distribution of acid corrosion conductivity, according to the characteristics of reservoir development, and finally make the residual acid flow back and put it into production. During this acid fracturing process, the volume of the fluid injected into the stratum amounts to 412m3, the volume of the preflush fluid is 136m3,
The acid used for cleaning wells is hydrochloric acid with a mass concentration of 10%, the displaced volume is 1.1-2.3m3/min, and the usage amount is 10-15% of the total amount of the acid-liquid combination.
Compared with the prior art, the invention has the following beneficial effects:
The invention has the characteristics such as high acid-liquid utilization efficiency, strong acid fracturing timeliness, long effective stable production time, and remarkable production-increasing effect, and is conducive to the stable and efficient development of high-temperature deep carbonate reservoirs.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG.1 shows the acid fracturing production curve of Well X.
FIG.2 is a schematic diagram of the effective closed pressure distribution in the acid corrosion cracks of Well Y when the stratum stress drops to 70%.
FIG.3 shows the influence of the effective closed stress of Well Y on the acid corrosion conductivity.
FIG.4 is a schematic diagram of the effective closed pressure distribution in the acid corrosion fractures after closure acidization of Well Y
FIG.5 shows the acid fracturing production curve of Well Y.
DETAILED DESCRIPTION OF THE INVENTION
The invention will be further described below based on the drawings and examples to help to understand it for a person skilled in the art. However, a person skilled in the art should note that the scope of the invention is not limited to specific implementation methods, as long as changes encountered are define by the appended claims and within the scope of the spirit and scope of the invention, they are all claimed by the invention.
Example 1 The reservoir in the well region where Well X is located has good homogeneity, with a thickness of 25-28m, but the water near the reservoir gathers and the barrier stress is low. In order to avoid leading to the lower water during the acid fracturing process on the basis of leading to the oil-gas storage space at the far-end of the well, the water-based fracturing fluid used to carry gel particles with a density slightly higher than that of the fracturing fluid is injected into the stratum, and the mineralization is controlled to 80g/L
during the injection process to ensure that the gel does not prematurely coagulate. After the gel particles reach the target position, the mineralization is adjusted to 10g/L, promoting the gel particles to absorb water and swell so as to form a high-strength gel barrier and increase the threshold of the stress through strata. The volume of the water-based guar gum fracturing fluid used in this process is 312.6m3, the volume of the gel particles is 7.6m3, and the displaced volume is 4.5m3/min. The construction scale, the liquid ratio and the displaced volume in construction are optimized for parameters to further improve the spatial distribution of acid corrosion conductivity, according to the characteristics of reservoir development, and finally make the residual acid flow back and put it into production. During this acid fracturing process, the volume of the fluid injected into the stratum amounts to 412m3, the volume of the preflush fluid is 136m3,
5 Date Recue/Date Received 2021-09-24 the volume of the conventional water-based fracturing fluid is 29m3,the volume of the gel acid is 218m3, the volume of the conventional acid is 29m3, and displaced volume of pumping the preflush fluid at the first stage is 6.1m3/min. After adopting the technical solution according to invention, the spatial distribution characteristics of the acid corrosion conductivity is better, and the maximum crack height does not exceed 20m. Compared with the production well adopting the conventional acid fracturing, the effective crack length is increased from 65m to 93m. FIG.1 shows the acid fracturing production curve of Well X. It can be seen from the figure that the initial output of Well X is 48t/d, and the average output within 250 days after the construction is 28.3t/d. The maximum daily output for the other production wells close to Well X had is 18.6t/d after design and construction according to the traditional method, and the average output within 160 days is 3.2t/d due to premature water breakthrough after construction. It can be seen that the invention effectively controls the crack height, increases the penetration distance of cracks, optimizes the spatial distribution characteristics of acid corrosion conductivity, and significantly improves the capacity of production and stable production time of production wells.
Example 2 Well Y is a horizontal development well with a horizontal section length of 450m. The well completion method is barefoot well completion. The horizontal well section has relatively complex lithological characteristics, various types of reservoirs unevenly distributed, and many different types of gas reservoirs. The permeability span ranges from 3.2 to 21.6mD, and the heterogeneity is strong. The well has undergone one acid fracturing at the early stage, and the initial daily oil production is 39.4m3/d, which drops to 1.8m3/d one month later. In order to improve the development level of the reservoir and ensure the production efficiency, a three-stage process temporarily hindering acidization is taken to the well section, regaining the crack conductivity, meanwhile, improving the production-increasing effect of acid on the low-permeability area, and optimizing the spatial distribution characteristics of the acid corrosion conductivity. The cellulose (6mm) used in the construction amounts to 600kg, added with 150kg, 200kg and 250kg, respectively, by 3 times. The respective liquid volume used for process temporarily hindering acidization at each stage is: gel acid (45m3) with hydrochloric acid concentration (10%), fracturing fluid (20m3), and temporary plugging liquid (20m3), among them, the displaced volume in construction of temporary plugging liquid is 1m3/min, and the displaced volume in construction of gel acid and fracturing liquid is 3m3/min. In addition, before a process temporarily hindering acidization, gel acid (40m3) is injected by displaced volume of 2m3/min to clean the well to ensure that the subsequent process temporarily hindering acidization smoothly undergoes; at the same time, in order to ensure the full dissolution of cellulose, after the process temporarily hindering acidization at the third stage is ended, gel acid (45m3) is injected for ending by displaced volume of 3m3/min. The total liquid volume for this construction is 340m3. After process temporarily hindering acidization for 10 minutes, residual acid flows back. After finishing the residual acid flowback, Well Y is put into production and on-site production data is monitored. When the formation pressure drops to 70% of the original formation pressure, a closed acidization process is taken for the reservoir. At this time, the closure pressure distribution in the acid corrosion crack is shown in FIG.2. It can be seen from the figure that the maximum converted closure pressure in the crack can reach 39.21MPa. FIG.3 shows the influence of the effective closed stress of Y
well on the acid corrosion conductivity. Combining FIG.3, it can be found that the maximum decrease of
Example 2 Well Y is a horizontal development well with a horizontal section length of 450m. The well completion method is barefoot well completion. The horizontal well section has relatively complex lithological characteristics, various types of reservoirs unevenly distributed, and many different types of gas reservoirs. The permeability span ranges from 3.2 to 21.6mD, and the heterogeneity is strong. The well has undergone one acid fracturing at the early stage, and the initial daily oil production is 39.4m3/d, which drops to 1.8m3/d one month later. In order to improve the development level of the reservoir and ensure the production efficiency, a three-stage process temporarily hindering acidization is taken to the well section, regaining the crack conductivity, meanwhile, improving the production-increasing effect of acid on the low-permeability area, and optimizing the spatial distribution characteristics of the acid corrosion conductivity. The cellulose (6mm) used in the construction amounts to 600kg, added with 150kg, 200kg and 250kg, respectively, by 3 times. The respective liquid volume used for process temporarily hindering acidization at each stage is: gel acid (45m3) with hydrochloric acid concentration (10%), fracturing fluid (20m3), and temporary plugging liquid (20m3), among them, the displaced volume in construction of temporary plugging liquid is 1m3/min, and the displaced volume in construction of gel acid and fracturing liquid is 3m3/min. In addition, before a process temporarily hindering acidization, gel acid (40m3) is injected by displaced volume of 2m3/min to clean the well to ensure that the subsequent process temporarily hindering acidization smoothly undergoes; at the same time, in order to ensure the full dissolution of cellulose, after the process temporarily hindering acidization at the third stage is ended, gel acid (45m3) is injected for ending by displaced volume of 3m3/min. The total liquid volume for this construction is 340m3. After process temporarily hindering acidization for 10 minutes, residual acid flows back. After finishing the residual acid flowback, Well Y is put into production and on-site production data is monitored. When the formation pressure drops to 70% of the original formation pressure, a closed acidization process is taken for the reservoir. At this time, the closure pressure distribution in the acid corrosion crack is shown in FIG.2. It can be seen from the figure that the maximum converted closure pressure in the crack can reach 39.21MPa. FIG.3 shows the influence of the effective closed stress of Y
well on the acid corrosion conductivity. Combining FIG.3, it can be found that the maximum decrease of
6 Date Recue/Date Received 2021-09-24 the acid corrosion conductivity is 56.7%. The closed acidification construction is divided into two parts:
first, injecting hydrochloric acid (10%) by displaced volume of 0.8m3/min under pressure of 40MPa for acid pickling; next sequentially injecting self-generating acid, gel acid, and hydrochloric acid with a mass concentration of 25% into the stratum for closed acidification by displaced volume of 2.1m3/min under pressure of 52MPa. In construction, the volume of the hydrochloric acid with a mass concentration of 10%
is 16m3, the volume of the hydrochloric acid with a mass concentration of 20%
is 60m3, the volume of gel acid is 70m3, and the volume of self-generating acid is 80m3, so the total liquid volume is 226m3. The effective closure pressure distribution of acid corrosion cracks after completion is shown in FIG.4. From FIG.4, it can be seen that the converted fracture closure pressure has dropped by more than 52.3%, and the overall acid corrosion conductivity has been improved and regained to 93.21%.
At the same time, the acid-liquid combination according to this technical solution is used for acidization, so that the spatial distribution of the acid corrosion conductivity is further optimized. FIG.5 shows the acid fracturing production curve of Well Y. It can be seen from FIG.5 that the initial oil production of Well Y is 105.6t/d after acid fracturing, and the average production within 150 days is 45.6t/d.
In addition, after production for 90 days, the daily oil production of Well Y can still be stable at about 40t/d for a long time, which fully reflects the optimization effect of this method on the timeliness of acid corrosion conductivity. For other production wells close to Well Y, after adopting conventional production-increasing measures, the initial oil production can reach 62t/d, but the daily oil production declines rapidly, and stabilizes at around 4.3t/d after 90 days, and the average production within 150 days is 12.6t/d.
The invention increases the volume of the oil-gas reserves where can be led by the production well by temporarily plugging the high-permeability area and definitely carrying out acid fracturing to the low-permeability area, and greatly improves the transportation capacity of the crack to oil-gas resources. At the same time, the invention takes into account the timeliness of the acid erosion conductivity, and carries out corresponding design and construction for it, which significantly optimizes the spatio-temporal distribution of the acid erosion conductivity, achieves high-efficiency acid-distributing to reservoirs, improves the development of reservoirs, makes the production well long-term stable and high-yield, and has important reference significance for on-site construction.
first, injecting hydrochloric acid (10%) by displaced volume of 0.8m3/min under pressure of 40MPa for acid pickling; next sequentially injecting self-generating acid, gel acid, and hydrochloric acid with a mass concentration of 25% into the stratum for closed acidification by displaced volume of 2.1m3/min under pressure of 52MPa. In construction, the volume of the hydrochloric acid with a mass concentration of 10%
is 16m3, the volume of the hydrochloric acid with a mass concentration of 20%
is 60m3, the volume of gel acid is 70m3, and the volume of self-generating acid is 80m3, so the total liquid volume is 226m3. The effective closure pressure distribution of acid corrosion cracks after completion is shown in FIG.4. From FIG.4, it can be seen that the converted fracture closure pressure has dropped by more than 52.3%, and the overall acid corrosion conductivity has been improved and regained to 93.21%.
At the same time, the acid-liquid combination according to this technical solution is used for acidization, so that the spatial distribution of the acid corrosion conductivity is further optimized. FIG.5 shows the acid fracturing production curve of Well Y. It can be seen from FIG.5 that the initial oil production of Well Y is 105.6t/d after acid fracturing, and the average production within 150 days is 45.6t/d.
In addition, after production for 90 days, the daily oil production of Well Y can still be stable at about 40t/d for a long time, which fully reflects the optimization effect of this method on the timeliness of acid corrosion conductivity. For other production wells close to Well Y, after adopting conventional production-increasing measures, the initial oil production can reach 62t/d, but the daily oil production declines rapidly, and stabilizes at around 4.3t/d after 90 days, and the average production within 150 days is 12.6t/d.
The invention increases the volume of the oil-gas reserves where can be led by the production well by temporarily plugging the high-permeability area and definitely carrying out acid fracturing to the low-permeability area, and greatly improves the transportation capacity of the crack to oil-gas resources. At the same time, the invention takes into account the timeliness of the acid erosion conductivity, and carries out corresponding design and construction for it, which significantly optimizes the spatio-temporal distribution of the acid erosion conductivity, achieves high-efficiency acid-distributing to reservoirs, improves the development of reservoirs, makes the production well long-term stable and high-yield, and has important reference significance for on-site construction.
7 Date Recue/Date Received 2021-09-24
Claims (8)
1. A highly efficient acid-distributing method considering spatio-temporal distribution characteristics of acid corrosion crack conductivity that sequentially comprises the following steps:
Sl. analyzing the structural feature, lithological characteristics, porosity type, physical characteristics and pressure-temperature characteristics of a carbonate reservoir stratum, based on seismic data and drilling data in blocks, so as to determine whether the following conditions exist:
a. the reservoir stratum being adjacent to the aquifer;
b. the crack expansion during the fracturing process being easy to cause the through-strata phenomenon , with small barrier stress difference between barriers;
c. the reservoir stratum having strong heterogeneity;
taking the measure to control crack height according to S2 if they exist but do not meet the conditions for acid fracturing construction, carrying out the acid fracturing construction according to S3 if they do not exist and meet the conditions for acid fracturing construction;
S2. taking the measure to control crack height, adopting artificial gel barrier technology controlling crack height, that is, injecting water-based fracturing fluid into a stratum with carrying the gel particles, which are cemented with each other to form a gel barrier, blunting the crack tip and increasing the resistance value of the upper and lower ends of the crack, further controlling the extension of crack height;
S3. carrying out the acid fracturing construction, by means of pumping with isochronous five-stage deceasing displaced volume, which includes the following processes:
Stage 1: pumping preflush fluid to press out the cracks and decreasing the formation temperature, wherein the pumped displaced volume at this stage is equal to the displaced volume of the conventional acid fracturing;
Stage 2: pumping gel acid, etching the crack wall more evenly with use of the characteristics that H+
is slowly released, wherein the pumped displaced volume at this stage is 80%
of the displaced volume of the conventional acid fracturing;
Stage 3: firstly pumping gel acid to supplement the H+ concentration in the crack, and then pumping non-reactive liquid so as to push the acid to etch the crack wall at the far end of a well, wherein the usage ratio of the gel acid and the non-reactive liquid at this stage is 4:1, and the pumped displaced volume at this stage is 60% of the displaced volume of the conventional acid fracturing;
Stage 4: using a combination of the gel acid and the non-reactive liquid acid, as the same as the pumping procedure in Stage 3, wherein the usage ratio of both liquid is 4:1, and the pumped displaced volume at this stage is 40% of the displaced volume of the conventional acid fracturing;
Stage 5: pumping conventional acid, wherein the pumped displaced volume at this stage is 20% of the displaced volume of the conventional acid fracturing;
Date Recue/Date Received 2021-09-24 S4. after completing the acid injection, adopting a three-stage process temporarily hindering acidization, the pumping procedures in each stage of the process temporarily hindering acidization being the same, that is, injecting temporary plugging fluid to effectively plug the high-permeability area and increasing the acid intake in the low-permeability area during the subsequent acidization process, using cellulose as temporary plugging material in the temporary plugging fluid, then injecting gel acid to fully dissolve the cellulose in the stratum and regaining the acid corrosion conductivity of the high-permeability area;
S5. At the production stage of oil-gas wells, as the formation pressure gradually decreases, slowly injecting a small amount of acid into the reservoir with low displaced volume to clean the well when the formation pressure drops to 70% of the original formation pressure, after cleaning the well, injecting an acid-liquid combination at the pressure slightly higher than that to open the cracks, the acid-liquid combination being self-generating acid + gel acid + hydrochloric acid, wherein the usage amount of the three acids is 40%, 35% and 25% of the total amount of the acid-liquid combination, respectively, the three acids are sorted into the self-generating acid, the gel acid and the hydrochloric acid according to the acid-rock reaction time from high to low, and injecting into the stratum in this order can improve the conductivity of the far-end, middle part and near-end of the cracks.
Sl. analyzing the structural feature, lithological characteristics, porosity type, physical characteristics and pressure-temperature characteristics of a carbonate reservoir stratum, based on seismic data and drilling data in blocks, so as to determine whether the following conditions exist:
a. the reservoir stratum being adjacent to the aquifer;
b. the crack expansion during the fracturing process being easy to cause the through-strata phenomenon , with small barrier stress difference between barriers;
c. the reservoir stratum having strong heterogeneity;
taking the measure to control crack height according to S2 if they exist but do not meet the conditions for acid fracturing construction, carrying out the acid fracturing construction according to S3 if they do not exist and meet the conditions for acid fracturing construction;
S2. taking the measure to control crack height, adopting artificial gel barrier technology controlling crack height, that is, injecting water-based fracturing fluid into a stratum with carrying the gel particles, which are cemented with each other to form a gel barrier, blunting the crack tip and increasing the resistance value of the upper and lower ends of the crack, further controlling the extension of crack height;
S3. carrying out the acid fracturing construction, by means of pumping with isochronous five-stage deceasing displaced volume, which includes the following processes:
Stage 1: pumping preflush fluid to press out the cracks and decreasing the formation temperature, wherein the pumped displaced volume at this stage is equal to the displaced volume of the conventional acid fracturing;
Stage 2: pumping gel acid, etching the crack wall more evenly with use of the characteristics that H+
is slowly released, wherein the pumped displaced volume at this stage is 80%
of the displaced volume of the conventional acid fracturing;
Stage 3: firstly pumping gel acid to supplement the H+ concentration in the crack, and then pumping non-reactive liquid so as to push the acid to etch the crack wall at the far end of a well, wherein the usage ratio of the gel acid and the non-reactive liquid at this stage is 4:1, and the pumped displaced volume at this stage is 60% of the displaced volume of the conventional acid fracturing;
Stage 4: using a combination of the gel acid and the non-reactive liquid acid, as the same as the pumping procedure in Stage 3, wherein the usage ratio of both liquid is 4:1, and the pumped displaced volume at this stage is 40% of the displaced volume of the conventional acid fracturing;
Stage 5: pumping conventional acid, wherein the pumped displaced volume at this stage is 20% of the displaced volume of the conventional acid fracturing;
Date Recue/Date Received 2021-09-24 S4. after completing the acid injection, adopting a three-stage process temporarily hindering acidization, the pumping procedures in each stage of the process temporarily hindering acidization being the same, that is, injecting temporary plugging fluid to effectively plug the high-permeability area and increasing the acid intake in the low-permeability area during the subsequent acidization process, using cellulose as temporary plugging material in the temporary plugging fluid, then injecting gel acid to fully dissolve the cellulose in the stratum and regaining the acid corrosion conductivity of the high-permeability area;
S5. At the production stage of oil-gas wells, as the formation pressure gradually decreases, slowly injecting a small amount of acid into the reservoir with low displaced volume to clean the well when the formation pressure drops to 70% of the original formation pressure, after cleaning the well, injecting an acid-liquid combination at the pressure slightly higher than that to open the cracks, the acid-liquid combination being self-generating acid + gel acid + hydrochloric acid, wherein the usage amount of the three acids is 40%, 35% and 25% of the total amount of the acid-liquid combination, respectively, the three acids are sorted into the self-generating acid, the gel acid and the hydrochloric acid according to the acid-rock reaction time from high to low, and injecting into the stratum in this order can improve the conductivity of the far-end, middle part and near-end of the cracks.
2.The highly efficient acid-distributing method considering spatio-temporal distribution characteristics of acid corrosion crack conductivity according to claim 1, wherein in S2 the pumped displaced volume is set to 3-7m3/min, the addition amount of gels is set to 20% of that of ceramcite, the mineralization range of the water-based fracturing fluid is set to be 0-100g/L for said artificial gel barrier technology.
3.The highly efficient acid-distributing method considering spatio-temporal distribution characteristics of acid corrosion crack conductivity according to claim 1, wherein in S3 said displaced volume of the conventional acid fracturing is 4-16m3/min, said preflush fluid system is 0.5%
of hydroxypropyl guar gum + fungicide + clay stabilizer + demulsifier + pH regulator, said gel acid system is 20% of HC1 + 0.8% of gel agent + 4% of corrosion inhibitor + 2% of demulsification and cleanup additive + 2% of iron ion stabilizer, the non-reactive liquid is conventional water-based fracturing fluid or formation water, the total liquid volume of acid fracturing constmction is 300-500 m3, amongst them, the usage amount of preflush fluid is 33% of the total liquid volume, the usage amount of the gel acid is 53% of the total liquid volume, and the usage amount of the water-based fracturing fluid or the formation water is 7%
of the acid-liquid combination, the usage amount of the conventional acid is 7% of the total liquid volume.
of hydroxypropyl guar gum + fungicide + clay stabilizer + demulsifier + pH regulator, said gel acid system is 20% of HC1 + 0.8% of gel agent + 4% of corrosion inhibitor + 2% of demulsification and cleanup additive + 2% of iron ion stabilizer, the non-reactive liquid is conventional water-based fracturing fluid or formation water, the total liquid volume of acid fracturing constmction is 300-500 m3, amongst them, the usage amount of preflush fluid is 33% of the total liquid volume, the usage amount of the gel acid is 53% of the total liquid volume, and the usage amount of the water-based fracturing fluid or the formation water is 7%
of the acid-liquid combination, the usage amount of the conventional acid is 7% of the total liquid volume.
4.The highly efficient acid-distributing method considering spatio-temporal distribution characteristics of acid corrosion crack conductivity according to claim 1, wherein in S4 said gel acid is 10% of HC1 +
0.8% of gel agent + 4% of corrosion inhibitor + 2% of demulsification and cleanup additive + 2% of iron ion stabilizer, 6mm of cellulose is used as temporary plugging material in the temporary plugging fluid, in which the fiber concentration is 1% ¨ 2%, the displaced volume of temporary plugging liquid is 1-3m3/min, the displaced volume of acid liquid is 2-7m3/min, and the strength of cellulose is 1.5-2.5kg/m.
0.8% of gel agent + 4% of corrosion inhibitor + 2% of demulsification and cleanup additive + 2% of iron ion stabilizer, 6mm of cellulose is used as temporary plugging material in the temporary plugging fluid, in which the fiber concentration is 1% ¨ 2%, the displaced volume of temporary plugging liquid is 1-3m3/min, the displaced volume of acid liquid is 2-7m3/min, and the strength of cellulose is 1.5-2.5kg/m.
5.The highly efficient acid-distributing method considering spatio-temporal distribution characteristics of acid corrosion crack conductivity according to claim 1, wherein in S4 the cellulose consumption is Date Recue/Date Received 2021-09-24 determined in combination with the length of the horizontal section and the maximum value allowable to ground equipment, the acid injection time after the temporary plugging at each stage is equivalent to the fiber dissolution time, so the usage amount of the acid liquid is calculated based on this.
6.The highly efficient acid-distributing method considering spatio-temporal distribution characteristics of acid corrosion crack conductivity according to claim 1, wherein in S4 in order to lower the ambient temperature and isolate the acid liquid from the fibers, high-viscosity fracturing fluid in sections is injected at beginning and ending of the temporary plugging fluid, respectively, and the usage amount for each injection is 50% of the temporary plugging fluid.
7.The highly efficient acid-distributing method considering spatio-temporal distribution characteristics of acid corrosion crack conductivity according to claim 1, wherein in S5 said self-generating acid is synthesized by reacting a carbonyl compound having high polymerization degree and a chlorine-containing organic ammonium salt by 1:1, said gel acid is the same as S3, said mass concentration of the hydrochloric acid is 20%, the displaced volume of injecting the acid-liquid combination is 1-4m3/min, and the total usage amount of the acid-liquid combination is 25% of the usage amount of the acid with the same type and concentration under conventional acid fracturing technology.
8.The highly efficient acid-distributing method considering spatio-temporal distribution characteristics of acid corrosion crack conductivity according to claim 1, wherein in S5 said acid used for cleaning wells is hydrochloric acid with a mass concentration of 10%, the displaced volume is 1.1-2.3m3/min, and the usage amount is 10-15% of the total amount of the acid-liquid combination.
Date Recue/Date Received 2021-09-24
Date Recue/Date Received 2021-09-24
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