四川盆地五峰组—龙马溪组异常地层压力成因与广义泊松比预测方法:以长宁地区为例

doi:10.13745/j.esf.sf.2020.12.2

摘要/Abstract

摘要：

将钻井实测四川盆地五峰组—龙马溪组地层压力与现今构造分区、青藏高原各块体的向东运动速度进行综合对比,发现五峰组—龙马溪组地层压力宏观压力背景可能受燕山运动以来多期构造运动的影响,超压区主要位于川东高陡构造带与川南低陡构造带的主体部位。燕山—喜山期,华蓥山断裂带东侧发生强烈挤压,形成长条形高陡背斜与开阔向斜相间分布。现今的青藏高原各块体向东运动也可能对五峰组—龙马溪组地层压力系数宏观分布产生一定的影响。钻井勘探证明,四川盆地五峰组—龙马溪组地层沉积后,地层中有机质先生成原油,在异常地温梯度作用下,裂解为天然气。所以,烃类裂解导致流体膨胀是五峰组—龙马溪组地层异常压力的第二个因素。同时,地层压力宏观背景下的局部地区地层压力异常可能是页岩气保存条件的反映。在对五峰组—龙马溪组地层压力异常成因分析的基础上,将地层压力异常抽象为水平作用力与垂向作用力,采用反映横向作用与垂向作用的地震泊松比参数作为地层压力预测的基础参数,从而建立起泊松比地层压力预测方法。实际资料预测与后期钻井验证证明,泊松比地层压力预测方法适合四川盆地五峰组—龙马溪组页岩气地层压力预测,经多年试验与改进,该方法已在威远—长宁地区页岩气田勘探开发中得到广泛推广与应用,产生了巨大的经济效益与社会效益。到2019年,长宁页岩气田累计产量已达130亿方,广义泊松比地层压力预测方法是助推长宁页岩气田成为我国第一页岩气田的关键技术之一。

关键词: 四川盆地长宁地区, 五峰组—龙马溪组;, 页岩气地层压力成因, 广义泊松比地层压力预测

Abstract:

We compared the measured pressure coefficient of the Wufeng-Longmaxi Formation, Sichuan Basin with the current tectonic division and the eastward movement velocity of the Qinghai-Tibet Plateau, and found that the formation pressure of the Wufeng-Longmaxi Formation might be affected by the multi-stage tectonic movement since the Yanshan Movement. The overpressure zone is located in the central areas of the high steep tectonic belt in eastern Sichuan and low steep tectonic belt in southern Sichuan. During the Yanshan-Xishan period, the east side of the Huayingshan fault zone was strongly extruded to form a long strip-shaped high steep anticline and an open syncline. The eastward movement of various blocks of the Qinghai-Tibet Plateau might also have influenced the pressure distribution in the Wufeng-Longmaxi Formation. Drilling results showed that after the deposition of the Wufeng-Longmaxi Formation in the Sichuan Basin, organic matters in the formation were transformed into crude oil and then cracked into natural gas under the action of abnormal geothermal gradient. Therefore, hydrocarbon cracking led to fluid expansion, which was the second causative factor of abnormal formation pressure in the Wufeng-Longmaxi Formation. Meanwhile, local abnormal formation pressure may reflect the shale gas preservation condition. Based on the analysis of the formation pressure anomaly in the Wufeng-Longmaxi Formation, the abnormal formation pressure was attributed to horizontal and vertical forces, and the Poisson’s ratio formation pressure prediction method was developed based on Poisson’s ratio calculation using seismic parameters. It is proved that this prediction method is suitable for predicting the shale gas formation pressure in the Wufeng-Longmaxi Formation. After years of testing and improvements, this prediction method has been widely applied in the exploration and development of shale gas fields in the Weiyuan-Changning area, bringing huge economic and social benefits. By 2019, the cumulative production of the Changning shale gas field has reached 13 billion cubic meters. The generalized Poisson’s ratio formation pressure prediction method is one of the key technologies propelling the Changning shale gas field to become the No.1 shale gas field in China.

Key words: Changning area, Sichuan Basin, Wufeng-Longmaxi Formation, shale gas formation pressure analysis, generalized Poisson’s ratio prediction;

中图分类号:

井翠, 郝龙, 张婧, 邓夏, 於文辉. 四川盆地五峰组—龙马溪组异常地层压力成因与广义泊松比预测方法:以长宁地区为例[J]. 地学前缘, 2021, 28(1): 402-410.

JING Cui, HAO Long, ZHANG Jing, DENG Xia, YU Wenhui. Genesis of the abnormal formation pressure in the Wufeng-Longmaxi Formation, Sichuan Basin and a generalized Poisson’s ratio prediction method: A case study of the Changning area[J]. Earth Science Frontiers, 2021, 28(1): 402-410.

图/表 10

图1 四川盆地五峰组—龙马溪组地层压力系数宏观分布与现今构造分区、沉积相带分布综合分析图(据文献[7,8,9,10]补充修改)

Fig.1 A schematic diagram showing the macro-distribution of the formation pressure coefficients and the current tectonic division in the Wufeng-Longmaxi Formation, Sichuan Basin and the distribution of sedimentary facies belts in the region. Modified from [7,8,9,10].

图2 四川盆地长宁地区五峰组—龙马溪组A、B井异常地层压力成因测井分析图

Fig.2 Log analysis of the abnormal formation pressure of Wells A and B in the Wufeng-Longmaxi Formation, Changning area, Sichuan Basin

图3 长宁地区钻井实测五峰组—龙马溪组地层压力与埋深关系图

Fig.3 Relationship between formation pressure and burial depth of the Wufeng-Longmaxi Formation, Changning area

图5 由图4页岩等效数字岩心开展的数字岩石物理模拟结果

Fig.5 Results of digital petrophysical simulation on the equivalent digital cores (shown in Fig.4) under different confining pressures. (1, 2) Variation ofPoisson’s ratio with pore pressure for 4% or 6% porosity; (3, 4) P- and S-wave velocity change with pore pressure for 4% or 6% porosity.

图4 过程法建立的五峰组—龙马溪组4%与6%二个孔隙度的页岩等效数字岩心

Fig.4 Composite illustration for the Wufeng-Longmaxi Formation. (1) Electron microscope images of shale rocks; (2) An equivalent digital core model built by the process method; (3) Equivalent digital cores with 4% (bottom) or 6% (top) porosity.

图6 钻井实测五峰组—龙马溪组A、B、E井地层压力系数与地震参数散点图

Fig.6 Scatter plots of formation pressure coefficient vs. seismic parameter measured in Wells A, B and E in the Wufeng-Longmaxi Formation, showing the variation trends

图7 长宁地区A、B、E井孔隙度、含气量与孔隙压力系数分析图

Fig.7 Results of drilling porosity, gas content and pressure coefficient analyses for wells A, B, and E in the Changning area. (1) Correlation between total gas content and porosity; (2-4) Plot of total gas content difference (left panel) or pressure coefficient difference (right panel) between indicated well pairs at different well layer

图8 长宁地区地层压力系数计算流程简图

Fig.8 Flow chart for calculating formation pressure coefficients of the Changning area

图9 泊松比地层压力预测方法在长宁地区的应用效果

Fig.9 Application of the Poisson’s ratio formation pressure prediction method in the Changning area (1)~(3) Calculated formation pressure coefficient contour maps showing three local formation pressure distributions in the Changing area.

表1 泊松比地层压力预测所得成果与实钻结果对比表(长宁地区)

Table 1 Comparison of Poisson’s ratio formation pressure prediction results and actual drilling results (Changning area)

项目	A	B	后验井C	后验井D
实钻结果	1.35	2.15	1.50	1.65
泊松比地层压力预测成果	1.38	2.17	1.51	1.63

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