CN102168545B - Coiled tubing supercritical CO2 jet fracturing method - Google Patents

Coiled tubing supercritical CO2 jet fracturing method Download PDF

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CN102168545B
CN102168545B CN 201110078618 CN201110078618A CN102168545B CN 102168545 B CN102168545 B CN 102168545B CN 201110078618 CN201110078618 CN 201110078618 CN 201110078618 A CN201110078618 A CN 201110078618A CN 102168545 B CN102168545 B CN 102168545B
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fracturing
liquid
fluid
supercritical
reservoir
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CN102168545A (en
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李根生
王海柱
沈忠厚
田守嶒
黄中伟
史怀忠
宋先知
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China University of Petroleum Beijing
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China University of Petroleum Beijing
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Abstract

The invention relates to a coiled tubing supercritical CO2 jet fracturing method. The method is used for performing jet fracturing on oil well reservoirs by taking supercritical CO2 as fracturing fluid. By the method, a supercritical CO2 fluid is used as the fracturing fluid to perform the jet fracturing; a supercritical CO2 sand jet perforating hole can reduce system pressure; the pressure needed by fissure extension can be further reduced by the characteristics of low viscosity and high dispersion performance of the supercritical CO2 fluid; most importantly, the supercritical CO2 jet fracturing does not pollute the reservoirs, but the supercritical CO2 can further improve the oil and gas recovery ratio after entering the reservoirs; the return discharge is not needed after the fracturing is completed; when the stage-by-stage jet fracturing is performed by using the coiled tubing, a tube pillar can be lifted or put down without mineshaft pressure relieving, the operation process is reduced and the operation cost is reduced, so that the method is extremely suitable for fracturing modification of unconventional oil-gas reservoirs such as thick oil reservoirs, low permeability and super-low permeability oil-gas reservoirs, shale gas reservoirs, coal bed methane reservoirs and the like of which the effects are low by using the conventional water-based fracturing fluid.

Description

The coiled tubing supercritical CO 2Spray fracturing process
Technical field
The present invention relates to a kind of oil well and spray fracturing process, relate in particular to a kind of coiled tubing supercritical CO 2Spray fracturing process, belong to the oil drilling field.
Background technology
Hydraulic fracturing technology proposes as far back as the forties in 20th century, be mainly used at that time old well reform, improve recovery ratio, hydraulic fracturing technology has become one of major measure of the unconventional oil-gas reservoir volume increase such as hypotonic special low-permeability oilfield, shale gas reservoir, bed gas reservoir at present.It utilizes ground high-pressure pump group, with the discharge capacity that surpasses stratum (reservoir) absorptive capacity, fracturing fluid is injected pit shaft, produce high pressure near the shaft bottom, when this pressure has overcome the tensile strength of the geostatic stress of Around A Borehole and rock, will make formation fracture and extend certain distance; Along with fracturing fluid continues to pump into, the crack continues forward to extend, and after the crack reached the requirement size, infusion was mixed with the load fluid of proppant, load fluid will continue the extension crack and with proppant transport in the crack; After the load fluid pumping is complete, the pumping gel breaker, the liquid that the glutinous fracturing liquid rubber-breaking of height is reduced to low-viscosity flows back to pit shaft, return and be discharged to ground, after pressure break finishes, only stay proppant in the crack and be used for the supporting crack wall like this, formed a crack passage with high flow conductivity.
As everyone knows, the purpose of fracturing is exactly to generate the crack passage with high flow conductivity, penetrates the injury district in nearly pit shaft area, makes oil well recover natural production capacity.Yet for above-mentioned traditional pressure break, need to inject a large amount of high glutinous fracturing fluids, also to pump into gel breaker subsequently, return discharge fracturing fluid, so not only cost is high again, and program is complicated, after the most important thing is that a large amount of water enters reservoir, can cause the reservoir secondary injury, reduce reservoir permeability, thereby reduce fracturing effect.Although multiple clean fracturing fluid occurred at present, reservoir pollution is alleviated to some extent reservoir secondary pollution in the time of still can't fundamentally thoroughly eliminating pressure break.
CO 2A kind of common gas, with its heat be forced into critical point more than (T c＞31.1 ℃, P c＞become supercritical CO 7.38MPa) time 2Fluid (SC-CO 2-super critical CO 2), under formation temperature and pressure condition, just can make CO more than general 750m 2Reach supercriticality.Supercritical CO 2Fluid both had been different from gas, also was different from liquid, and it has close to the low-viscosity of gas and high diffusibility, close to the high density of liquid and surface tension is the characteristic such as zero.If with CO 2Be used for the injection pressure break of oil well, these above-mentioned characteristics can make supercritical CO 2Spray broken rock and have higher efficient and lower broken rock thresholding pressure, its low glutinous characteristic, will help CO in fracturing process simultaneously 2Fluid Flow in A easily produces many and complicated crack in reservoir.Coiled tubing can Operating Pressure, removes conveniently, therefore, if with supercritical CO 2Fluid and coiled tubing combine and carry out reservoir and spray pressure break and can greatly reduce the pressure break cost, improve fracturing effect.
Summary of the invention
For solving the problems of the technologies described above, the object of the present invention is to provide a kind of oil reservoir to spray fracturing process, it is to adopt coiled tubing delivering liquid CO 2, make it become supercritical CO bottom oil well 2And reservoir is sprayed the method for pressure break, have an efficiency of breaking rock of injection high, the characteristics such as broken rock thresholding pressure is low, and flow chart is few, and the pressure break cost is low.
For achieving the above object, the invention provides a kind of coiled tubing supercritical CO 2Spray the method for pressure break, it is with supercritical CO 2For fracturing fluid, reservoir is sprayed the method for pressure break.
Above-mentioned coiled tubing supercritical CO provided by the present invention 2The method of spraying pressure break can comprise the following steps:
Clear well is processed: utilize clear water or flushing fluid circulation well cleanup, and use the drift size gauge tool drifting;
Perforation is processed: with liquid CO 2Mutually be mixed to get fluid-mixing with jet with abrasive material, by coiled tubing, fluid-mixing be transported in oil well, and carry out abrasive perforating by the injection fracturing device in oil well and make reservoir produce the duct;
Frac treatment: after the eliminating impurities with the oil well bottom, continue the pure liquid CO of input 2, this liquid state CO 2To change supercritical CO at the pit shaft certain depth 2Fluid also carries out pressure break to reservoir, makes reservoir produce the crack;
Support and process: proppant is sneaked into liquid CO 2In, make it with liquid CO 2Enter in the crack that produces, when the proppant that enters the crack reaches predetermined quantity, stop sneaking into proppant, stop pumping into liquid CO 2, complete one section fracturing work.
According to concrete technical scheme of the present invention, above-mentioned injection fracturing process provided by the present invention is applicable to only carry out one section pressure break, also go for carrying out the pressure break more than two sections, when carrying out the pressure break of multistage, need to isolate crack and the duct of pressure break, to avoid liquid CO in follow-up fracturing work 2Pour in the first paragraph crack, insulating liquid will have higher viscosity and low filtration property, infiltrate reservoir when reducing the second segment pressure break as far as possible, require simultaneously fracturing fluid aquation voluntarily after after a while at a certain temperature, so that the row of returning after pressure break is complete, insulating liquid of the present invention can be this area insulating liquid commonly used, for example guanidine glue, water base natural plant gum insulating liquid.When having completed the final stage fracturing work, when no longer carrying out pressure break, needn't carry out again isolation processing.According to concrete technical scheme of the present invention, preferably, said method is further comprising the steps of:
Isolation processing: input insulating liquid, shutoff crack and duct;
To carry on coiled tubing to next section pressure break position, then repeat perforation processing, frac treatment and support treatment step, complete next section fracturing work.
After completing the final stage fracturing work, no longer need to carry out isolation processing, can directly carry out next step operation, particularly, when the pressure break reservoir in oil well is heavy crude reservoir or coal bed gas, shale gas reservoir, after frac treatment, can carries out vexed well and process and (make supercritical CO 2Fully act on viscous crude, reduce Crude viscosity, perhaps fully replace CH in coal bed gas and shale gas reservoir 4After opening well and making production again), namely said method also comprises the step that the row of returning processes or vexed well is processed; When the pressure break reservoir in oil well is the conventional gas and oil Tibetan, can directly produce, need not the row's of returning processing or vexed well and process.
In above-mentioned fracturing process provided by the invention, the CO that adopts 2Originate more extensive, can be by CO 2The gas field directly obtains, and perhaps extracts (being conducive to like this environmental protection) from the tail gas of the generations such as power plant, steel mill, due to supercritical CO 2CO during pressure break 2Consumption is not very large, can be by CO 2Tank car transports, CO 2Storage tank preferably can pressure-bearing 10MPa the left and right, guarantee CO 2Be in liquid state under certain temperature and pressure, also need to have insulation effect simultaneously, keep the low temperature that needs in storage tank.CO 2Can install as required refrigeration unit additional on tank car, guarantee in transportation and pump into the front needs of fracturing unit truck.CO 2Transport pressure generally can be controlled at 3-5MPa, temperature is controlled at-20 ℃ to 5 ℃, can guarantee like this to transport safely.In order to guarantee better liquid CO 2State, preferably, be stored in CO 2Liquid CO in tank car 2Pressure may be controlled to 4-5MPa, temperature may be controlled to-10 ℃ to 5 ℃.
Conventional fracturing unit just can carry out supercritical CO through simple modifications 2At first pressure break changes the heavy chemicals sealing mats such as rubber in pipe valve, high-pressure pump, downhole tool into metallic gasket, and main cause is, CO 2Penetrability is very strong, can be penetrated in the rubber-like macromolecular material, and overlong time just can be stung leakage rubber cushion; Secondly, install cooling back installation additional on the high-pressure pump pump head on fracturing unit truck, the temperature general control prevents piston and sleeve frictional heat 0-3 ℃ of left and right, makes liquid CO 2Vaporization affects pump efficiency.
When carrying out fracturing work, at the well head place, the liquid CO in coiled tubing 2Be in the cryogenic high pressure liquid state, along with liquid CO 2Descending gradually, its temperature and pressure also raises gradually, when temperature and pressure simultaneously during postcritical, and liquid CO 2Change supercritical CO into 2, supercritical CO 2Produce high-pressure spray injection reservoir with the fluid-mixing of abrasive material through the nozzle that sprays fracturing device, make reservoir produce the duct.Due to temperature rising gradually along with the increase of the degree of depth on stratum, temperature gradient is about 20-50 ℃/km, will be over CO in the local temperature that underground hundreds of rice is dark 2Critical-temperature (31.1 ℃), the required pressure of concurrent fracturing is generally higher, is easy to reach CO 2Critical pressure (7.38MPa), therefore, usually just can realize supercritical CO at down-hole 750m 2Spray pressure break.And when stratum temperature anomaly, or when the superficial part formation breakdown can't reach critical-temperature, can be at ground liquid towards CO 2Fluid heats, and namely injection fracturing process provided by the present invention can also be included in the perforation processing inputting the liquid CO of coiled tubing 2The step that the fluid-mixing that forms with the jet abrasive material heats; This heat treated can be carried out on ground.
According to concrete technical scheme of the present invention, preferably, perforation is processed can comprise following concrete steps:
To be stored in CO by pipeline 2Liquid CO in tank car 2Be transported to fracturing blender truck, with jet abrasive material and liquid CO 2Mix, then be transported to fracturing unit truck through high pressure line; By fracturing unit truck (quantity of fracturing unit truck can increase and decrease according to the discharge capacity needs) with liquid CO 2Send into coiled tubing with the fluid-mixing that abrasive mixed is combined into via high pressure line with jet, and the injection fracturing device that arrives the oil well bottom carries out abrasive perforating and makes reservoir produce the duct.In fluid-mixing in perforation is processed, the jet that adopts may be controlled to account for the 5-8wt% of fluid-mixing weight with the addition of abrasive material, the jet that adopts can be this area jet abrasive material commonly used with abrasive material, and for example fineness is 60 orders-120 purpose pomegranate stone sand or quartz sand.
In above-mentioned fracturing process provided by the invention, preferably, frac treatment can comprise the following steps:
The well mouth of oil well place arranges the annulus back pressure valve, and reasonable control well mouth pressure (generally can be controlled at 5-8MPa) makes the CO of oil well bottom 2With eliminating impurities (carrying smoothly pit shaft outside), even become the CO of supercriticality bottom oil well 2By annular space (space between coiled tubing and pit shaft is called annular space), abrasive material and the landwaste that perforation produces carried out pit shaft; Then closed loop backlash pressure valve, continue the pure liquid CO of input by coiled tubing 2Perhaps input simultaneously pure liquid CO by coiled tubing and annular space 2, this liquid state CO 2Become supercritical CO in oil well 2Fluid, this supercritical CO 2Fluid enters the duct, and reservoir is carried out pressure break, makes reservoir produce the crack.
In above-mentioned fracturing process provided by the invention, when carrying out fracturing work, for duct and the crack of pressure break supporting processing, preferably, support to process comprising the following steps:
When fracture extension after predetermined length (in the art, according to different geological conditions and needs of production, can be scheduled to different pressure break length, determine thus more of the fracturing fluid pressure break time of pumping and discharge capacity, generally, the pressure break time of each section fracturing work may be controlled to 10-30 minute, pump output may be controlled to 5-9 side/minute), but be not limited to this scope), by fracturing blender truck, proppant is sneaked into liquid CO 2In, make it with liquid CO 2Enter in the crack that produces, fracture is supported; When the proppant that enters the crack reaches predetermined quantity, stop sneaking into proppant, stop inputting liquid CO 2, complete one section fracturing work.In supporting processing, preferably, the addition of the proppant that adopts may be controlled to account for liquid CO 2With the 5-20wt% of proppant quality sum, the liquid CO here 2Refer to the liquid CO that pumps into simultaneously with proppant 2, the proppant that adopts can be this area proppant commonly used, is preferably the hollow ceramic proppant.
The present invention adopts supercritical CO 2Fluid sprays pressure break as fracturing fluid, has following advantages:
1, supercritical CO 2The injection efficiency of breaking rock is high, and broken rock thresholding pressure is low, therefore can be at supercritical CO 2Add the jet abrasive material in fluid, carry out casing sidetracking and spray pressure break, not only reduced system's injection pressure requirement, and the safety that has improved pressing crack construction.
2, supercritical CO 2Fluid viscosity is lower, has high diffusion property, even flow in the coiled tubing of reduced size, its frictional resistance is also very little, is very easy to flow, and simultaneously, in the original microcrack of reservoir, high glutinous fracturing fluid can't enter, and supercritical CO 2Fluid can arbitrarily flow, and helps the transmission of pressure in pit shaft, reduces frac system pressure, more can make reservoir produce many and complicated microcrack, forms fracture network in reservoir, connects pit shaft, improves well yield and recovery ratio.
3, supercritical CO 2Reservoir without any pollution, is not contained solid phase particles not moisture yet, when it enters reservoir, can avoid hole to shout the generation of the harm such as obstruction, reservoir clay swelling, rock wettability reversal, water-sensitive, simultaneously, under its superpower solvability effect, supercritical CO 2Can dissolve heavy oil component and other pollutants of near wellbore zone, reduce near wellbore zone gas stream dynamic resistance, therefore, supercritical CO 2After the injection pressure break is complete, need not to inject gel breaker and also need not the row of returning, can directly go into operation, not only reduce flow chart, reduce costs, but also can prevent proppant backflow pit shaft in the crack; In addition, if reservoir Crude Oil viscosity is higher, can also select vexed well, make supercritical CO 2Fully act on crude oil, increase reservoir energy, reduce viscosity of crude, strengthen its mobility, thereby further improve oil recovery factor.
4, supercritical CO 2The surface tension of fluid is zero, can enter into any greater than supercritical CO 2The space of molecule is simultaneously for rammell and coal seam, CO 2Molecule and its adsorption capacity are much larger than CH 4Molecule, so when carrying out shale gas reservoir and bed gas reservoir pressure break, supercritical CO 2Enter reservoir can also displacement sorption gas content up to 85% coal bed gas and shale gas, further improve the gentle well production of gas deposit recovery efficiency, the most important thing is that this class gas reservoir permeability is extremely low, the leak-off less, more be conducive to the formation in crack, therefore be very suitable for the fracturing reform of shale gas reservoir, bed gas reservoir, DAMAGE OF TIGHT SAND GAS RESERVOIRS.
5, supercritical CO 2Fluid is combined with coiled tubing when carrying out the multi-injection pressure break, need not pressure release in upper lifting pipe post process, and coiled tubing is Operating Pressure directly, saves operation and time.
Description of drawings
The following drawings only is intended to the present invention is done and schematically illustrates and explain, not delimit the scope of the invention.Wherein:
Fig. 1 is the coiled tubing supercritical CO 2Spray the staged fracturing schematic flow sheet;
Fig. 2 is abrasive perforating schematic diagram before the first paragraph pressure break;
Fig. 3 is the pressure break mode schematic diagram of first paragraph pressure break;
Fig. 4 is another the mode schematic diagram that presses off the crack;
Fig. 5 is the input mode schematic diagram of buying insulating liquid after has pressed in the first paragraph crack;
Fig. 6 is the schematic diagram of the another kind of input mode of insulating liquid;
Fig. 7 is abrasive perforating mode schematic diagram before the second segment pressure break;
Fig. 8 is the pressure break mode schematic diagram of second segment pressure break;
Fig. 9 is the row's of returning mode schematic diagram of insulating liquid;
Figure 10 is the schematic diagram of another row's of returning mode of insulating liquid;
Figure 11 is the vexed well of the row's of returning insulating liquid schematic diagram to be produced not;
Figure 12 is the coiled tubing supercritical CO with the ground heater 2Spray the staged fracturing schematic flow sheet.
The drawing reference numeral explanation:
1CO 2Tank car 2 vehicular refrigeration unit 3CO 2Adiabatic high pressure line 5 fracturing blender truck 6 fracturing unit truck 7 coiled tubing 8 roller of continuous oil pipe 9 coiled tubing injection head 10 wellhead assembly 11 ring control back-pressure valve 12 borehole wall 13 annular space 14 ground 15 injection fracturing tool 16 supercritical COs of storage tank 4 220 reservoir 21 ground heating device 22 cracks, jet 17 eyelet 18 spray-hole 19 shaft bottom
The specific embodiment
Understand for technical characterictic of the present invention, purpose and beneficial effect being had more clearly, referring now to Figure of description, technical scheme of the present invention is carried out following detailed description, but but can not be interpreted as restriction to practical range of the present invention.
Embodiment
Coiled tubing supercritical CO provided by the invention 2Spray fracturing process and introduce supercritical CO 2Fluid can be given full play to supercritical CO as fracturing liquid 2With the advantage separately of coiled tubing, the method can comprise following concrete steps:
1, clear well is processed:
Use the jack rabbit drifting, carry out well-flushing with clear water or flushing fluid (this area flushing fluid commonly used gets final product), prevent that instrument is hampered or meets card on the one hand, prevent also that on the other hand in pit shaft, foreign material enter deep formation in fracturing process, pollute reservoir;
2, perforation is processed:
Figure 1 shows that the coiled tubing supercritical CO 2Spray the staged fracturing schematic flow sheet, when carrying out the first paragraph abrasive perforating, first fracturing tool 15 is lowered into the predetermined level in shaft bottom 19, error is no more than 0.5 meter;
Liquid CO 2By the CO that adds refrigeration unit 2 2Tank car 1 transportation, transport pressure is controlled at 4-5MPa, and temperature is controlled at-10 ℃ to 5 ℃;
CO 2Liquid CO in storage tank 3 2Be transported to fracturing blender truck 5 through adiabatic high pressure line 4, fracturing blender truck 5 is with jet abrasive material and liquid CO 2Be transported to fracturing unit truck 6 after fully being mixed to get fluid-mixing;
Liquid CO 2Become high-pressure mixing fluid with the fluid-mixing of abrasive material after through fracturing unit truck 6 pressurizations with jet, be delivered directly to coiled tubing 7, coiled tubing 7 is transported to Downhole jetting fracturing tool 15 through roller of continuous oil pipe 8, coiled tubing injection head 9, wellhead assembly 10 and pit shaft 13 with high-pressure mixing fluid successively; When needs heat high-pressure mixing fluid, can ground heating device 21 be set after fracturing unit truck 6, as shown in figure 12;
The supercritical CO of high pressure 2With the fluid-mixing spray-hole 18 generation high speed abradant jets 16 through spray fracturing tool 15 of jet with abrasive material, penetrate sleeve-penetrating (cased hole completion) or directly act on the eyelet (duct) 17 that reservoir 20 (barefoot completion) generates certain size, as shown in Figure 2; Space between coiled tubing 7 and the borehole wall 12 is annular space, can control the annular space base pressure by annulus back pressure valve 11 is set; When abrasive perforating, annulus back pressure valve 11 should be adjusted to a suitable position, makes the supercritical CO in shaft bottom 2Density is in optimum range, and (general control is at 700kg/m 3Above), improve abrasive perforating efficient, also to guarantee that the foreign material such as landwaste that perforation generates and abrasive material waste residue can be by supercritical CO simultaneously 2Fluid is carried pit shaft 13 outside through annular space, arrives ground 14;
3, frac treatment:
After abrasive perforating was complete, fracturing blender truck 5 quit work, closed loop backlash pressure valve 11, continue large discharge capacity (may be controlled to 5-9 side/minute, the time of each section frac treatment may be controlled to 10-30 minute, is preferably 20 minutes) pump into liquid CO 2, it is entered in eyelet 17, reservoir 20 is carried out pressure break, make crack 22 generate and extend at the stress concentrated position of reservoir eyelet 17;
4, support processing:
When the length in crack 22 reaches pre-provisioning request, open fracturing blender truck 5, begin to pump into the pressure break proppant, as shown in Figure 3; Due to supercritical CO 2Fluid viscosity is lower, compare with conventional aqueous fracturing fluid, it is relatively poor that it holds the sand ability under the arm, (this discharge capacity can be determined according to the way of this area routine according to actual conditions also to need larger discharge capacity when therefore pumping into proppant, generally can be controlled at 5-9 side/minute), the guarantee proppant enters the crack root smoothly like this, realizes effective support in crack.For CO 2Gas, the high pressure supercritical CO 2After spray-hole 18 ejections, pressure sharply reduces, and the volume rapid expanding produces joule-Thomson cooling effect, make the Around Jet reduces heat, when the temperature got below freezing point, will freeze as water, to spraying fracturing effect and bringing safely adverse effect, therefore want strict Control Nozzle pressure drop and discharge capacity in spraying fracturing process, avoid the shaft bottom to freeze as far as possible, can take to reduce the coiled tubing flow pressure from annular space and the common infusion mode of coiled tubing, as shown in Figure 4;
5, isolation processing:
When first paragraph crack proppant pump into complete after, stop pumping into CO 2, pump into a small amount of insulating liquid, crack 22 and the eyelet 17 of shutoff first paragraph pressure break, CO when preventing from carrying out the second segment pressure break 2Pour in the crack 22 of first paragraph pressure break, the insulating liquid of this moment requires to have higher viscosity and low filtration property, infiltrate reservoir as far as possible when reducing the second segment formation breakdown, require simultaneously its aquation voluntarily after section sometime at a certain temperature, so as pressure break complete after the row of returning; The infusion method as shown in Figure 5 and Figure 6, Fig. 5 directly injects from coiled tubing, if the insulating liquid viscosity is higher, frictional resistance is larger, can select annular space method for implanting shown in Figure 6;
6, second segment fracturing work:
Insulating liquid is after the injection of the crack of first paragraph pressure break is complete, on carry coiled tubing 7 to next section pressure break position (but coiled tubing 7 Operating Pressures, the loaded down with trivial details steps such as common tubing string pressure release makes up a joint have been saved), repeat perforation, pressure break and support and process, carry out second segment and spray pressure break (as shown in Figure 7 and Figure 8);
Needn't squeeze into again insulating liquid after the final stage pressure break is complete, the row's of returning insulating liquid after the insulating liquid aquation of squeezing into before this; A large amount of CO during due to pressure break 2Therefore enter reservoir, for reservoir has replenished enough energy, the row of returning is comparatively easy, even if the Depleted Reservoirs of the exploiting the later stage also row of returning smoothly, the row's of returning mode can be selected any mode in Fig. 9 and mode shown in Figure 10;
If the reservoir of pressure break is heavy crude reservoir or shale gas reservoir, bed gas reservoir, the row's of returning insulating liquid (the isolation liquid measure is considerably less, and is very little on the reservoir permeability impact) not after pressure break is taked the method for vexed well, makes the CO that enters reservoir 2Fully act on viscous crude, reduce viscosity, reduce the crude oil flow resistance, perhaps with shale gas reservoir and bed gas reservoir in CH 4Displacement reaction fully occurs, and improves free CH in gas reservoir 4Content, vexed well opening well and making production after a period of time, output and recovery ratio all will improve greatly.
Supercritical CO 2Spray pressure break raising oil recovery factor and well yield mechanism as follows:
1, supercritical CO 2Fluid density is large, and very strong solvability is arranged, and it can dissolve heavy oil component and other organic matters of near wellbore zone, reduces near wellbore zone gas stream dynamic resistance;
2, supercritical CO 2Fluid viscosity little (near the gas viscosity), diffusivity is strong, and easily diffusion in reservoir crude oil, makes the crude oil volume expansion, reduces Crude viscosity, increases crude oil fluidity, simultaneously supercritical CO 2Surface tension of liquid is zero, easily enters any space greater than its molecule, is conducive to the displacement of reservoir oil;
3, supercritical CO 2Do not contain aqueous water in fluid, the reservoir medium clay soil is expanded, can also make on the contrary fine and close clay sand bed dehydration, open the sand bed duct, reduce borehole wall skin factor;
4, in fracturing process, a large amount of CO 2Infiltrate reservoir, for reservoir provides energy, increase the crude oil flow ability, significantly reduce oil water interfacial tension, reduce residual oil saturation, thereby improve oil recovery factor;
5, utilize supercritical CO 2When spraying fracturing reform shale gas reservoir and bed gas reservoir, due to CO 2Be better than CH with the adsorption capacity of rock 4With the adsorption capacity of rock, CO 2Entering can the CH of displacement sorption on rammell and coal seam after reservoir 4, increase free state CH 4Content, thus output and recovery ratio improved, also can realize CO 2Bury protection of the environment;
6, supercritical CO 2Fracturing fluid belongs to clean fracturing fluid, to reservoir without any injury, need not the row of returning after pressure break, do not have residue yet, protected reservoir, simplified flow chart;
7, supercritical CO 2The characteristics such as low glutinous easily diffusion can make reservoir produce many and complicated microcrack, increase drainage area.
Rationally determining of injection drop:
For CO 2Gas, through after throttle nozzle, pressure sharply reduces, and the volume rapid expanding produces joule-Thomson cooling effect, makes the nozzle ambient temperature sharply reduce, and low temperature can make the shaft bottom water freezing, causes potential safety hazard to spraying pressure break.Temperature drop and gas discharge capacity, nozzle diameter, nozzle upstream and downstream pressure, nozzle upstream CO 2The relating to parameters such as temperature, so want the above parameter of choose reasonable in fracturing process, the below illustrates.
Suppose that 1900m well depth place nozzle upstream temperature is that 340K is invariable, nozzle downstream (shaft bottom) pressure is 10MPa, and nozzle diameter is 4mm, and examination is calculated at nozzle upstream pressure and is respectively 14,18,22, nozzle downstream temperature during 26MPa.
According to formula Just can obtain the nozzle downstream temperature.Through the CO that tables look-up 2K value (isentropic index) be 1.28, downstream temperature when the substitution corresponding data can calculate the different spray nozzles upstream temperature, as shown in table 1:
T dn---nozzle downstream temperature, K; T up---nozzle upstream temperature, K; P dn---nozzle downstream pressure, MPa; P up---nozzle upstream pressure, MPa.
Table 1
Upstream pressure (MPa) 14 18 22 26 27.2
Downstream temperature (K) 315.87 298.98 286.14 275.87 273.15
By the data of table 1 as can be known, when nozzle upstream pressure reached 27.2MPa, bottom hole temperature (BHT) just can be down to freezing point, and namely under these conditions, the nozzle maximum differential pressure is designed to 17.2MPa.In actual fracturing process, can reduce injection pressure by reducing pumpage, thereby reduce nozzle pressure reduction, those skilled in the art can determine according to the size of needed pressure reduction the size of pumpage, generally may be controlled to 5-9 side/minute.
Above-described specific embodiment; purpose of the present invention, technical scheme and beneficial effect are further described; institute is understood that; the above is only specific embodiments of the invention; the protection domain that is not intended to limit the present invention; within the spirit and principles in the present invention all, any modification of making, be equal to replacement, improvement etc., within all should being included in protection scope of the present invention.

Claims (10)

1. coiled tubing supercritical CO 2Spray the method for pressure break, it is with supercritical CO 2For fracturing fluid, oil reservoir is sprayed the method for pressure break, the method comprises the following steps:
Clear well is processed: utilize clear water or flushing fluid circulation well cleanup, and use the drift size gauge tool drifting;
Perforation is processed: with liquid CO 2Mutually be mixed to get fluid-mixing with jet with abrasive material, by coiled tubing, fluid-mixing be transported in oil well, and carry out abrasive perforating by the injection fracturing device in oil well and make reservoir produce the duct;
Frac treatment: after the eliminating impurities with the oil well bottom, continue the pure liquid CO of input 2, this liquid state CO 2Become supercritical CO in oil well 2Fluid also carries out pressure break along described duct to reservoir, makes reservoir produce the crack;
Support and process: proppant is sneaked into liquid CO 2In, make it with liquid CO 2Enter in the crack that produces, when the proppant that enters the crack reaches predetermined quantity, stop sneaking into proppant, stop inputting liquid CO 2, complete one section fracturing work;
Isolation processing: input insulating liquid, shutoff crack and duct;
To carry on coiled tubing to next section pressure break position, then repeat perforation processing, frac treatment and support treatment step, complete next section fracturing work.
2. method according to claim 1, wherein, when the pressure break reservoir in oil well was heavy crude reservoir or coal bed gas, shale gas reservoir, the method was included in also that the row of returning after frac treatment processes or the step of vexed well processing.
3. method according to claim 1, wherein, described perforation is processed and is comprised following concrete steps:
To be stored in CO by pipeline 2Liquid CO in tank car 2Be transported to fracturing blender truck, with jet abrasive material and liquid CO 2Be mixed to get fluid-mixing, then be transported to fracturing unit truck through high pressure line;
By fracturing unit truck with liquid CO 2Send into coiled tubing with the fluid-mixing that abrasive material forms via high pressure line with jet, and the injection fracturing device that arrives the oil well bottom carries out abrasive perforating and makes reservoir produce the duct.
4. according to claim 1 or 3 described methods, wherein, in described fluid-mixing, described jet accounts for the 5-8wt% of described fluid-mixing weight with the addition of abrasive material.
5. method according to claim 4, wherein, described jet abrasive material is that fineness is 60 orders-120 purpose pomegranate stone sand.
6. method according to claim 3, wherein, be stored in CO 2Liquid CO in tank car 2Pressure be 3-5MPa, temperature is-20 ℃ to 5 ℃.
7. method according to claim 1, wherein, described frac treatment comprises the following steps:
The well mouth of oil well place arranges the annulus back pressure valve, and well head pressure is controlled at 5-8MPa, makes the CO of oil well bottom 2With eliminating impurities;
Continue the pure liquid CO of input by coiled tubing 2Perhaps input simultaneously pure liquid CO by coiled tubing and annular space 2, this liquid state CO 2To change supercritical CO in a certain degree of depth of pit shaft 2Fluid, this supercritical CO 2Fluid enters the duct and reservoir is carried out pressure break, makes reservoir produce the crack.
8. method according to claim 1, wherein, described support is processed and is comprised the following steps:
After predetermined length, by fracturing blender truck, proppant is sneaked into liquid CO when fracture extension 2In, make it with liquid CO 2Enter in the crack that produces, fracture is supported;
When the proppant that enters the crack reaches predetermined quantity, stop sneaking into proppant, stop inputting liquid CO 2, complete one section fracturing work;
The addition of described proppant accounts for described liquid CO 25-20wt% with described proppant quality sum.
9. method according to claim 8, wherein, described proppant is the hollow ceramic proppant.
10. method according to claim 1, wherein, the method also be included in perforation process in liquid towards CO 2The step that the fluid-mixing that forms with abrasive material with jet heats.
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