CN111852465B - Evaluation method for obtaining shale reservoir rock core original water content by water-based mud drilling - Google Patents
Evaluation method for obtaining shale reservoir rock core original water content by water-based mud drilling Download PDFInfo
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- CN111852465B CN111852465B CN202010876130.7A CN202010876130A CN111852465B CN 111852465 B CN111852465 B CN 111852465B CN 202010876130 A CN202010876130 A CN 202010876130A CN 111852465 B CN111852465 B CN 111852465B
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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
- E21B49/00—Testing the nature of borehole walls; Formation testing; Methods or apparatus for obtaining samples of soil or well fluids, specially adapted to earth drilling or wells
- E21B49/005—Testing the nature of borehole walls or the formation by using drilling mud or cutting data
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
- Y02A10/00—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE at coastal zones; at river basins
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Abstract
An evaluation method for obtaining the original water content of shale reservoir cores by water-based mud drilling belongs to the field of shale gas exploration and development. The method for obtaining the water content of the shale reservoir core by water-based mud drilling comprises the following steps: (1) the method comprises the steps of (1) cleaning a complete column sample of a shale reservoir rock core just drilled and rapidly freezing the complete column sample to be below zero; (2) freezing and drilling a column sample with the diameter of 2.5cm from the edge to the center of the core complete column by liquid nitrogen; (3) cutting rock samples with different distances from the center point of the complete core column sample from the column sample with the diameter of 2.5 cm; (4) respectively measuring the mass of the materials, drying the materials for 12 hours at 200 ℃ under the condition of approximate vacuum, and then respectively measuring the mass of the materials; (5) determining the water content of the rock samples by the mass of the rock samples before and after drying; (6) and analyzing the water content change characteristics of the shale reservoirs and determining the original water content of the shale reservoirs by combining the distance from the center point of the complete core column sample.
Description
Technical Field
The invention relates to a method for evaluating the original water content of a shale reservoir core obtained by water-based mud drilling, and belongs to the technical field of shale gas exploration and development.
Background
Shale gas is natural gas aggregation which is mainly formed in shale formations with hydrocarbon production capability in an adsorption and free state, and free gas and adsorption gas are two main occurrence modes of shale gas in shale reservoirs. The adsorption gas is mainly endowed on the inner surface of the nanoscale pores through physical adsorption, in particular to the inner surface of the organic matter nanopores and the inner surface of the nanopores contributed by clay minerals. The free gas mainly exists in the pore space which is not occupied by adsorbed gas and pore water, such as cracks, macropores, small pore centers and the like of the shale reservoir. For the sea shale reservoir with high maturity in the south of China, the pores do not contain liquid hydrocarbon. The pore space in shale reservoirs is mainly occupied by adsorbed gas, free gas, pore water and the like. The pore water content in the shale gas directly affects the shale gas content. The pore fluid water not only occupies a part of pore volume to directly influence the free shale gas quantity, but also occupies the adsorption position on the inner surface of the pore so as to reduce the shale gas quantity of the shale reservoir occurrence adsorption state. Shale gas enrichment is generally relatively low in shale reservoirs with high water content, while organic-rich shale reservoirs with lower water content are more likely to be enriched with shale gas. Shale gas reservoir water content is an important parameter for evaluating shale gas enrichment degree and carrying out shale gas resource amount calculation.
At present, the relative water content of different intervals of a shale reservoir is generally evaluated through a logging curve, specific water content values cannot be accurately evaluated, and the cost is relatively high. In addition, the in situ coring process, whether it is water-based mud or oil-based mud drilling, can affect the water content of the core to some extent, causing variations in the original water content through the core. In addition, the core is taken out and then subjected to the processes of cleaning, airing, acceptance checking, warehousing and storage and the like. These also affect the original moisture content of the core, which in turn causes some deviation in the moisture content analyzed by the core. In recent years, with the progress of technology and the increase of environmental protection pressure, the application range of water-based mud drilling fluid is more and more wide, and water-based mud drilling fluid is gradually used for replacing oil-based mud drilling fluid in the drilling process of shale intervals. In order to better evaluate shale gas reservoirs, how to evaluate the original water content of a core sample obtained in a water-based mud drilling process is a problem to be solved.
Therefore, the invention provides a method for evaluating the original water content of the core of the shale reservoir obtained by water-based mud drilling, which evaluates the original water content of the core sample obtained by utilizing water-based mud drilling fluid and provides important parameters for better evaluating the characteristics of the shale reservoir and calculating the shale gas resource amount.
Disclosure of Invention
The purpose of the invention is that: the method for evaluating the original water content of the core of the shale reservoir obtained by water-based mud drilling is provided, and the original water content of the core sample is obtained when water-based mud drilling fluid is evaluated. Overcomes the defects of the prior art that the method can not accurately and quantitatively evaluate and has high cost.
The technical scheme adopted by the invention is as follows: a method for evaluating the original water content of shale reservoir cores obtained by water-based mud drilling is characterized by comprising the following steps:
step 1: in a drilling site, a complete core column sample of a shale reservoir just drilled is not cleaned and quickly frozen to be below zero, and the state of water-based slurry drilling fluid in the core is fixed;
step 2: selecting an interval without developing cracks by utilizing a liquid nitrogen freezing rock sample drilling technology, and drilling a small column sample with the diameter of 2.5cm from the edge to the center of a complete core column sample;
step 3:rock samples with different distances from the center point of the complete core column sample are cut from small column samples with the diameter of 2.5cm, the height ranges of the rock samples are 0.5cm to 1.0cm, and the distances from the center point of the complete core column sample are respectively D 1 、D 2 、...、D n The unit of the distance from the intercepted rock sample to the center point of the complete core column sample is cm, and n is the number of intercepted rock sample samples;
step 4: the mass of the intercepted rock sample samples is measured respectively, then the rock sample samples are dried for 12 hours at the temperature of 200 ℃ under the condition of approximate vacuum, the mass of the rock sample samples is measured respectively after the drying is finished, and the mass of the rock sample samples before the drying is m respectively 1 0 、m 2 0 、...、m n 0 The mass after drying is m respectively 1 、m 2 、...、m n The unit of the sample mass is g, and n is the number of the intercepted rock sample samples;
step 5: from the mass of these intercepted rock sample samples before and after drying, their water content was calculated according to the following formula
W i =( m i 0 - m i )/ m i ×100%
In which W is i Is the water content of the intercepted ith rock sample, the unit is m i 0 And m i The weight of the intercepted ith rock sample before and after drying is g;
step 6: according to the characteristic that the water content of the intercepted rock sample changes along with the distance from the center point of the complete core column sample, determining the original water content of the shale reservoir, in an intersection graph of the water content and the distance from the center point of the complete core column sample, when the water content change amplitude of the intercepted rock sample is smaller along with the distance from the center point of the complete core column sample and finally tends to be stable, the stable value of the water content is the original water content of the shale reservoir, when the water content change amplitude of the intercepted rock sample is smaller along with the distance from the center point of the complete core column sample, but does not tend to be stable, fitting the existing data in the intersection graph of the water content and the distance from the center point of the complete core column sample, and the value of the water content tends to be stable on the fitting curve is the original water content of the shale reservoir.
The invention has the beneficial effects that: the method for evaluating the original water content of the core of the shale reservoir obtained by water-based mud drilling realizes that the original water content of the core sample is obtained when water-based mud drilling fluid is evaluated. Overcomes the defects of the prior art that the method can not accurately and quantitatively evaluate and has high cost. The raw water content of the shale reservoir core evaluated is an important parameter necessary in shale gas exploration and development.
Drawings
Fig. 1 is a flow chart of the present invention.
Fig. 2 is a graph showing the characteristic of the water content of a rock sample according to the embodiment 1 of the present invention as a function of distance from the center point of a complete core column.
Fig. 3 is a graph showing the characteristic of the water content of the rock sample according to the embodiment 2 of the present invention as a function of distance from the center point of the complete core column.
The specific embodiment is as follows:
example 1: as shown in fig. 1, a method for evaluating the original water content of a shale reservoir core obtained by water-based mud drilling comprises the following steps:
step 1: and in the drilling site, the complete core column sample of the shale reservoir just drilled is not cleaned and quickly frozen to be below zero, and the state of the water-based mud drilling fluid in the core is fixed.
Step 2: and selecting an interval without developing cracks by utilizing a liquid nitrogen freezing rock sample drilling technology, and drilling a small column sample with the diameter of 2.5cm from the edge to the center of the complete core column sample.
Step 3: 9 rock samples with different distances from the center point of the complete core column sample are cut from a small column sample with the diameter of 2.5cm, the height ranges of the rock samples are 0.5cm to 1.0cm, and the distances from the center point of the complete core column sample are 5.5cm, 4.8cm, 4.1cm, 3.4cm, 2.7cm, 2.0cm, 1.3cm, 0.6cm and 0cm respectively.
Step 4: the mass of the intercepted rock sample was measured separately, and then dried at 200 ℃ under near vacuum for 12 hours, after the drying was completed, the mass of these rock sample before drying was 7.44g, 7.30g, 7.03g, 6.78g, 6.92g, 6.94g, 6.64g, 6.70g and 6.66g, respectively, the mass after drying was 6.76g, 6.81g, 6.68g, 6.57g, 6.79g, 6.85g, 6.56g, 6.62g and 6.58g, respectively, the unit of the sample mass was g, and n was the number of the intercepted rock sample.
Step 5: from the mass of these intercepted rock sample samples before and after drying, their water contents were calculated to be 10.04%, 7.15%, 5.26%, 3.22%, 1.95%, 1.26%, 1.22%, 1.20% and 1.20% respectively according to the following formulas,
W i =( m i 0 - m i )/ m i ×100%
in which W is i Is the water content of the intercepted ith rock sample, the unit is m i 0 And m i The weight of the intercepted ith rock sample before and after drying is g.
Step 6: as shown in fig. 2, according to the characteristic that the water content of the intercepted rock sample changes along with the distance from the center point of the complete core column sample, the original water content of the shale reservoir is determined, in the intersection graph of the water content and the distance from the center point of the complete core column sample, the water content change amplitude of the intercepted rock sample is smaller along with the distance from the center point of the complete core column sample, and finally the water content tends to be stable, and the stable value of the water content is 1.20%, namely the original water content of the shale reservoir.
Example 2: as shown in fig. 1, a method for evaluating the original water content of a shale reservoir core obtained by water-based mud drilling comprises the following steps:
step 1: and in the drilling site, the complete core column sample of the shale reservoir just drilled is not cleaned and quickly frozen to be below zero, and the state of the water-based mud drilling fluid in the core is fixed.
Step 2: and selecting an interval without developing cracks by utilizing a liquid nitrogen freezing rock sample drilling technology, and drilling a small column sample with the diameter of 2.5cm from the edge to the center of the complete core column sample.
Step 3: 9 rock samples with different distances from the center point of the complete core column sample are cut from a small column sample with the diameter of 2.5cm, the height ranges of the rock samples are 0.5cm to 1.0cm, and the distances from the center point of the complete core column sample are 5.5cm, 4.8cm, 4.1cm, 3.4cm, 2.7cm, 2.0cm, 1.3cm, 0.6cm and 0cm respectively.
Step 4: the mass of the intercepted rock sample was measured separately, and then dried at 200 ℃ under near vacuum for 12 hours, after the drying was completed, the mass of these rock sample before drying was 7.44g, 7.30g, 7.03g, 6.78g, 6.92g, 6.94g, 6.64g, 6.70g and 6.66g, respectively, the mass after drying was 6.76g, 6.81g, 6.68g, 6.57g, 6.79g, 6.85g, 6.56g, 6.62g and 6.58g, respectively, the unit of the sample mass was g, and n was the number of the intercepted rock sample.
Step 5: from the mass of these intercepted rock sample samples before and after drying, their water contents were calculated to be 10.04%, 7.15%, 5.26%, 3.22%, 1.95%, 1.26%, 1.22%, 1.20% and 1.20% respectively according to the following formulas,
W i =( m i 0 - m i )/ m i ×100%
in which W is i Is the water content of the intercepted ith rock sample, the unit is m i 0 And m i The weight of the intercepted ith rock sample before and after drying is g.
Step 6: as shown in fig. 3, according to the characteristic that the water content of the intercepted rock sample changes along with the distance from the center point of the complete core column sample, the original water content of the shale reservoir is determined, the variation amplitude of the water content of the intercepted rock sample changes along with the distance from the center point of the complete core column sample, but finally the intercepted rock sample does not tend to be stable, the water content tends to be stable on a fitting curve by fitting the existing data in an intersection graph of the water content and the distance from the center point of the complete core column sample, and the value when the water content tends to be stable is about 1.21%, namely the original water content of the shale reservoir.
Claims (1)
1. A method for evaluating the original water content of shale reservoir cores obtained by water-based mud drilling is characterized by comprising the following steps:
step 1: in a drilling site, a complete core column sample of a shale reservoir just drilled is not cleaned and quickly frozen to be below zero, and the state of water-based slurry drilling fluid in the core is fixed;
step 2: selecting an interval without developing cracks by utilizing a liquid nitrogen freezing rock sample drilling technology, and drilling a small column sample with the diameter of 2.5cm from the edge to the center of a complete core column sample;
step 3: rock samples with different distances from the center point of the complete core column sample are cut from small column samples with the diameter of 2.5cm, the height ranges of the rock samples are 0.5cm to 1.0cm, and the distances from the center point of the complete core column sample are respectively D 1 、D 2 、...、D n The unit of the distance from the intercepted rock sample to the center point of the complete core column sample is cm, and n is the number of intercepted rock sample samples;
step 4: the mass of the intercepted rock sample samples is measured respectively, then the rock sample samples are dried for 12 hours at the temperature of 200 ℃ under the condition of approximate vacuum, the mass of the rock sample samples is measured respectively after the drying is finished, and the mass of the rock sample samples before the drying is m respectively 1 0 、m 2 0 、...、m n 0 The mass after drying is m respectively 1 、m 2 、...、m n The unit of the sample mass is g, and n is the number of the intercepted rock sample samples;
step 5: from the mass of these intercepted rock sample samples before and after drying, their water content was calculated according to the following formula
W i =( m i 0 - m i )/ m i ×100%
In which W is i Is the water content of the intercepted ith rock sample, the unit is m i 0 And m i The weight of the intercepted ith rock sample before and after drying is g;
step 6: according to the characteristic that the water content of the intercepted rock sample changes along with the distance from the center point of the complete core column sample, determining the original water content of the shale reservoir, in an intersection graph of the water content and the distance from the center point of the complete core column sample, when the water content change amplitude of the intercepted rock sample is smaller along with the distance from the center point of the complete core column sample and finally tends to be stable, the stable value of the water content is the original water content of the shale reservoir, when the water content change amplitude of the intercepted rock sample is smaller along with the distance from the center point of the complete core column sample, but does not tend to be stable, fitting the existing data in the intersection graph of the water content and the distance from the center point of the complete core column sample, and the value of the water content tends to be stable on the fitting curve is the original water content of the shale reservoir.
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