A quantitative method for the marine recharge source of formation water in gas reservoirs

Abstract

The present invention discloses a quantitative method for the marine replenishment source of formation water in a gas reservoir, comprising the following steps: selecting a marine formation area with anhydrite as a target area; surveying and determining the deposition thickness of anhydrite in the target area; selecting anhydrite samples in the drilling core of the target area, and detecting the water content of the anhydrite samples; collecting drilling data, determining the replenishment radius; and obtaining the replenishment amount of the marine replenishment source of formation water in combination with the deposition thickness of anhydrite, the water content of anhydrite, and the replenishment radius. The present invention is applied to the overall exploration and development of gas reservoirs and the drilling geological design and construction. The method has the characteristics of being specific, effective, and feasible. It has important practical significance for determining the macroscopic occurrence form and distribution law of formation water in gas reservoirs and the overall exploration and development of gas reservoirs in the future. It can further provide empirical data and method reference for future exploration and development of gas reservoirs, and has broad application prospects.

Description

Technical Field

[0001] The invention relates to the field of oil and natural gas exploration and development, and in particular to a quantitative method for determining the marine replenishment source of formation water in a gas reservoir. Background Art

[0002] Formation water coexists with oil and gas in different forms in the pores, caves and cracks of underground rocks. It is a participant in the generation of oil and gas, an important driving force and carrier for the migration, accumulation and accumulation of oil and gas, and contains rich information on sedimentation, diagenesis and accumulation. Formation water in oil and gas fields is one of the key factors affecting the development of gas fields. Once water is found in gas wells, the gas permeability of the reservoir will be reduced, and the gas production will drop rapidly, seriously affecting the production capacity of gas reservoirs. At the same time, due to the long geological history of some gas reservoirs, multiple tectonic periods, widespread diagenetic transformation, severe reservoir densification, unclear accumulation mechanisms and patterns, uncertain water-producing strata, and different water volumes, the distribution characteristics of formation water and gas-water are very complex, which directly limits the in-depth understanding and comprehensive grasp of the occurrence form and distribution law of formation water in gas reservoirs.

[0003] There are usually four sources of formation water: one is sedimentary water, which refers to the water preserved in the sediment during the accumulation process, and its salt content and chemical composition are controlled by the original environment; the second is infiltration water, which refers to surface water that penetrates into the rock layer such as atmospheric precipitation, and the infiltration water can dilute the highly mineralized underground water; the third is deep water, which refers to the highly mineralized and high-temperature water originating from deep in the earth's crust; the fourth is conversion water, which refers to the interlayer water released by clay transformation during the sedimentary diagenesis and hydrocarbon formation process, and the water decomposed when organic matter is converted into hydrocarbons.

[0004] With the continuous exploitation of deep gas reservoirs, the intrusion (recharge) of deep marine formation water has gradually intensified, resulting in the inability of some wells to meet production needs during water flooding and well sealing during drilling and exploitation. At the same time, due to the long-term evaporation and evolution of seawater, quantitative analysis is no longer possible. This has greatly increased the difficulty of gas reservoir development, exploration, and prediction. As time goes by, the contradiction will become more prominent. Therefore, scientific and technological research to determine the characteristics of gas reservoir formation water recharge is imminent.

[0005] The study found that due to the evaporation of seawater in a long-term arid environment, a thick layer of gypsum (CaSO4·2H2O) will be deposited. When the burial depth of the marine gypsum layer is greater than 3,000 meters, the marine gypsum layer will be dehydrated and converted into anhydrite (CaSO4) under compaction and diagenesis. In the late stage of diagenesis, gypsum dehydration is the main source of replenishment of formation water for gas reservoirs. Summary of the invention

[0006] The purpose of the present invention is to overcome the problem that the prior art cannot quantitatively analyze the recharge of gas reservoir formation water, and to provide a quantitative method for the marine phase recharge source of gas reservoir formation water. The present invention quantitatively obtains the recharge amount of the marine phase recharge source of gas reservoir formation water by analyzing the thickness and dehydration amount of anhydrite in the target area of ​​the marine strata.

[0007] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0008] A quantitative method for determining the marine replenishment source of formation water in a gas reservoir comprises the following steps:

[0009] An area of ​​marine strata with anhydrite was selected as the target area;

[0010] Surveying and determining the thickness of anhydrite deposits in the target area;

[0011] Selecting anhydrite samples from the drilling core of the target area, and detecting the water content of the anhydrite samples;

[0012] Collect drilling data and determine the recharge radius;

[0013] The recharge amount of the marine recharge source of formation water is obtained by combining the deposition thickness of anhydrite, the water content of the anhydrite sample and the recharge radius.

[0014] The method of the present invention utilizes the gypsum layer formed after seawater deposition. When the gypsum layer reaches a certain depth, it will be dehydrated and converted into anhydrite. By analyzing the thickness and dehydration amount of anhydrite in the marine strata in the target area, the replenishment radius is determined in combination with drilling data, and the replenishment amount (contribution) of the marine replenishment source of the gas reservoir formation water is quantitatively obtained. This is a specific, effective and feasible quantitative method for the marine replenishment source of formation water. The present invention has important practical significance for determining the macroscopic occurrence form and distribution law of gas reservoir formation water and the overall exploration and development of gas reservoirs in the future. Through the present invention, it can further provide empirical data and method reference for future gas reservoir exploration and development.

[0015] Furthermore, the method for selecting a marine stratum area with anhydrite as a target area is as follows: the stratum lithology of the target area is of marine origin, the stratum sedimentary lithology is mainly carbonate rock and sulfate rock, and there is no chloride deposition.

[0016] Furthermore, the natural gamma value of anhydrite is extremely low, ranging from 1.5 to 6 API, the apparent resistivity of anhydrite is 7000Ω·m to 20000Ω·m and the high apparent resistivity is abnormal, the neutron porosity of anhydrite is close to zero, ranging from -2 to 1; the thorium-uranium ratio in anhydrite is relatively high, ranging from >4, and the uranium-potassium ratio is low, ranging from <2.

[0017] Furthermore, the method for determining the deposition thickness of anhydrite in the target area is: determining the deposition thickness of anhydrite or the proportion of anhydrite in the core based on drilling core or logging data.

[0018] Furthermore, the method for detecting the water content of the anhydrite sample is: using a full-diameter nuclear magnetic resonance core analyzer to detect the water content of the anhydrite sample to obtain the water content of the anhydrite sample.

[0019] Furthermore, the recharge radius is determined according to the relationship between the permeability coefficient and the recharge radius, which is the combination of Formula 1 and Formula 2;

[0020]

[0021] Where R is the recharge radius, m; Q is the water production, m 3 / d; S is the vertical depth of drilling, m; M is the deposition thickness of anhydrite, m; r is the radius of the water-producing well, m; K is the permeability coefficient, m / d.

[0022] Furthermore, the calculation formula for the replenishment amount is:

[0023] Rb=SqM(Gg-Gh)(3)

[0024] Where Rb is the replenishment amount, m 3 ; Sq is the area after adding the replenishment radius, Sq = π (r + R) 2 , m 2 ; M is the deposition thickness of anhydrite, m; Gg is the water content of gypsum, %; Gh is the water content of the anhydrite sample, %.

[0025] Furthermore, according to the theoretical gypsum molecular formula CaSO4·2H2O, the theoretical water content in the gypsum is 20.93%, which is used as the gypsum water content. When the gypsum layer is completely converted into anhydrite, the original gypsum water content cannot be obtained, and the gypsum water content is calculated according to the theoretical gypsum molecular formula.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The method of the present invention analyzes the thickness and water content of anhydrite in the target area, determines the recharge radius in combination with drilling data, and quantitatively obtains the recharge amount of the marine recharge source of the formation water in the gas reservoir. It is a quantitative method for the marine recharge source of the formation water. The present invention is applied to the overall exploration and development of gas reservoirs and the method of drilling geological design and construction. It has the characteristics of being specific, effective and feasible. It has important practical significance for determining the macroscopic occurrence form and distribution law of formation water in gas reservoirs and the overall exploration and development of gas reservoirs in the future. It can further provide empirical data and method reference for future exploration and development of gas reservoirs, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic flow diagram of a quantitative method for determining the marine replenishment source of formation water in a gas reservoir according to the present invention;

[0029] Figure 2 Schematic diagram of the target area structure according to an embodiment of the present invention

[0030] Figure 3 is a lithology and lithofacies description diagram of each layer according to an embodiment of the present invention;

[0031] Figure 4 is a drilling and logging results curve diagram according to an embodiment of the present invention;

[0032] Figure 5 is a cross-sectional schematic diagram of a drilling connection according to an embodiment of the present invention;

[0033] Figure 6 It is a gas production curve diagram of Well No. 2 according to an embodiment of the present invention. DETAILED DESCRIPTION

[0034] The present invention is further described in detail below in conjunction with test examples and specific implementation methods. However, this should not be understood as the scope of the above subject matter of the present invention being limited to the following embodiments, and all technologies realized based on the content of the present invention belong to the scope of the present invention.

[0035] Example 1

[0036] like Figure 1 As shown, a quantitative method for determining the marine recharge source of formation water in a gas reservoir comprises the following steps:

[0037] An area of ​​marine strata with anhydrite was selected as the target area;

[0038] Surveying and determining the thickness of anhydrite deposits in the target area;

[0039] Selecting anhydrite samples from the drilling core of the target area, and detecting the water content of the anhydrite samples;

[0040] Collect drilling data and determine the recharge radius;

[0041] The recharge amount of the marine recharge source of formation water was obtained by combining the deposition thickness of anhydrite, the water content of the anhydrite samples, and the recharge radius.

[0042] The technical indicators of the present invention for selecting an area with marine strata deposition as the target area are: the strata lithology of the target area is marine in origin, the strata sedimentary lithology is mainly carbonate rock and sulfate rock, and there is no chloride deposition. The natural gamma value of anhydrite is extremely low, the natural gamma value is 1.5-6API, the apparent resistivity of anhydrite is 7000Ω·m-20000Ω·m and the high apparent resistivity is abnormal, the neutron porosity of anhydrite is close to zero, the thorium-uranium ratio in anhydrite is relatively high, the range is>4, and the uranium-potassium ratio is low, the range is<2.

[0043] In this embodiment, through geological data analysis, the Xinchang structural zone in the Sichuan Basin is considered to be an area where marine strata (anhydrite) are deposited. Figure 2 In this example, three target areas are selected, namely Well No. 1, Well No. 2, and Well No. 3. Taking Well No. 2 as an example, the studied strata are mainly the fourth section of the Leikoupo Formation. Figure 3 The upper part of the fourth section of the Leikoupo Formation in the Middle Triassic is composed of light gray and gray powder crystal (algae mass) dolomite and gypsum (hard gypsum) dolomite; the middle part is composed of (gypsum-containing) microcrystalline dolomite and (gypsum-containing) mud crystal dolomite interbedded with white gypsum rock; the lower part is composed of gray microcrystalline dolomite, mud crystal dolomite and gray-white hard gypsum rock interbedded with unequal to equal thickness. The hard gypsum in Well No. 2 is analyzed, and the geophysical characteristics are as follows: Figure 4 The specific parameters are shown in Table 1. It is worth noting that since the apparent resistivity of rock formations varies greatly with porosity, water content, temperature, and density, the apparent resistivity in different regions is different; the high or low apparent resistivity can only represent the relative high or low of different rock formations in a region, and cannot be generalized; therefore, the low apparent resistivity of 7000Ω·m to 20000Ω·m mentioned above is only a general situation, but there may also be apparent resistivity values ​​greater than 20000Ω·m.

[0044] Table 1 List of skeleton parameters of various rock components

[0045] Lithology sandstone Solution White Cloud Anhydrite Illite Natural Gamma (API) 40-75 10 8 1.5-6 130-235 Acoustic time difference (us / ft) 55.5 47.5 43.5 50.5 90 Neutron porosity (%) -3.5 0 2.0 -2.0 35.2 <![CDATA[Density (g / cm 3 )]]> 2.65 2.71 2.87 2.98 2.63 Photoelectric cross section index (b / e) 1.81 5.08 3.14 5.06 3.45 Apparent resistivity (Ω·m) --- >1000 >1000 >10000 ---

[0046] The method for surveying and determining the sedimentary thickness of the marine strata in the target area is: determine the sedimentary thickness of anhydrite in the core or the proportion of anhydrite based on the drilling core or logging data. The burial depth of anhydrite is greater than 3,000 meters. If the drilling core drills into the anhydrite layer, the sedimentary thickness of the anhydrite can be determined directly based on the drilling core; if the drilling core of some wells does not reach the corresponding target depth, the sedimentary thickness of the anhydrite in the core can be determined based on the logging data or the proportion of anhydrite in the formation multiplied by the formation thickness to obtain the sedimentary thickness of the anhydrite. The proportion of anhydrite in each target area is, for example, Figure 5 shown.

[0047] The water content of the anhydrite sample is detected by using the full-diameter nuclear magnetic resonance core analyzer AniMR-Hole Core in the mobile station laboratory to detect the anhydrite sample in the drilling core of the selected target area to obtain the water content of the anhydrite sample.

[0048] The supply radius is determined jointly by formula 1 and formula 2;

[0049]

[0050] Where R is the recharge radius, m; Q is the water production, m 3 / d; S is the vertical depth of the well, m; M is the deposition thickness of anhydrite, m; r is the radius of the water production well, m; K is the permeability coefficient, m / d. The water production, vertical depth of the well, radius of the water production well, and permeability coefficient are all based on the actual measured values ​​during the drilling test or production process.

[0051] The formula for calculating the replenishment amount is:

[0052] R b =S q M(G g -G h ) (3)

[0053] Where R b is the supply amount, m 3 ; S q is the area after adding the replenishment radius, S q =π(r+R) 2 , m 2 ; M is the thickness of the marine strata, m; G g is the water content of gypsum, %; G h is the water content of the anhydrite sample, %. In some embodiments, when the gypsum layer is completely converted into anhydrite, the original gypsum water content cannot be obtained. According to the theoretical gypsum molecular formula CaSO4·2H2O, the theoretical water content in the gypsum is 20.93%, which is used as the gypsum water content.

[0054] The method of the present invention is used to calculate the recharge amount for the three selected target areas, and the calculation results are shown in Table 2.

[0055] Table 23 Recharge volume of target areas

[0056]

[0057] In addition, the actual water production of Well No. 2 is as follows Figure 6 As shown, based on the recharge volume of the marine recharge source of formation water determined above, combined with the actual water production of Well 2, an analysis is conducted to provide data support for the next step of gas reservoir exploration and development.

[0058] In this embodiment, three target areas are selected, and the water content of the anhydrite samples in the target areas is detected to be 0, indicating that all the gypsum is converted into anhydrite. However, gypsum is not converted into anhydrite in other marine strata. The water content of anhydrite is greater than 0. There are marine strata deposits in the area. The marine supply source of the gas reservoir formation water can be calculated according to the method of the present invention.

[0059] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for quantifying the source of marine replenishment of formation water in a gas reservoir, characterized in that: The following steps are involved: An area of ​​marine strata with anhydrite was selected as the target area; Surveying and determining the thickness of anhydrite deposits in the target area; Selecting anhydrite samples from the drilling core of the target area, and detecting the water content of the anhydrite samples; Collect drilling data and determine the recharge radius; Combining the deposition thickness of anhydrite, the water content of the anhydrite sample, and the recharge radius, the recharge amount of the marine recharge source of formation water is obtained; The recharge radius is determined according to the relationship between the permeability coefficient and the recharge radius. The relationship between the permeability coefficient and the recharge radius is: Where R is the recharge radius, m; Q is the water production, m 3 / d; S is the vertical depth of the well, m; M is the deposition thickness of anhydrite, m; r is the radius of the water-producing well, m; K is the permeability coefficient, m / d; The formula for calculating the replenishment amount is: R b =S q M(G g -G h ) Where R b is the supply amount, m 3 ; S q is the area after adding the replenishment radius, S q =π(r+R) 2 , m 2 ; M is the deposition thickness of anhydrite, m; G g is the water content of gypsum, %; G h is the water content of the anhydrite sample, %.

2. The method for quantifying the marine replenishment source of gas reservoir formation water according to claim 1, characterized in that: The method for selecting a marine stratum area with anhydrite as a target area is as follows: the stratum lithology of the target area is of marine origin, the stratum sedimentary lithology is mainly carbonate rock and sulfate rock, and there is no chloride deposition.

3. The method for quantifying the marine replenishment source of gas reservoir formation water according to claim 2, characterized in that: The natural gamma value of anhydrite ranges from 1.5 to 6 API, the apparent resistivity of anhydrite ranges from 7000Ω·m to 20000Ω·m, the neutron porosity of anhydrite ranges from -2 to 1, the thorium to uranium ratio in anhydrite is greater than 4, and the uranium to potassium ratio is less than 2.

4. The method for quantifying the marine replenishment source of gas reservoir formation water according to claim 1, characterized in that: The method for determining the deposition thickness of anhydrite in the target area is: determining the deposition thickness of anhydrite in the core based on drilling core or logging data, or obtaining the deposition thickness of anhydrite by multiplying the proportion of anhydrite in the formation by the formation thickness.

5. The method for quantifying the marine replenishment source of gas reservoir formation water according to claim 1, characterized in that: The water content of the anhydrite sample is detected by using a full-diameter nuclear magnetic resonance core analyzer.

6. The method for quantifying the marine replenishment source of gas reservoir formation water according to claim 1, characterized in that: According to the theoretical gypsum molecular formula CaSO4·2H2O, the theoretical water content in gypsum is 20.93%, which is taken as the gypsum water content.

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