致密碳酸盐岩气藏裂缝预测与主控因素分析——以四川盆地高石梯地区灯影组储层为例

Prediction of fractures in tight carbonate gas reservoirs and analysis of main controlling factors:a case study on Dengying formation reservoir of Gaoshiti block in the Sichuan Basin

天然裂缝是致密碳酸盐岩气藏重要的储集空间和渗流通道,定量预测其发育程度与分布规律、揭示主控地质因素,对气藏开发具有重要实践意义。本文以四川盆地中部乐山—龙女寺古隆起的高石梯地区灯影组致密碳酸盐岩储层为研究对象,在裂缝参数表征基础上建立应力场-能量-裂缝参数的计算模型,结合多期裂缝叠加算法定量预测裂缝发育分布规律,并重点分析了岩性、断层和构造形态对裂缝发育的影响。结果表明:①高石梯地区灯影组储层裂缝表现为张剪缝为主、高角度缝、半充填特征,裂缝优势走向为NW-SE与近N-S方向,裂缝密度在0~2条/m,高值区主要分布在断层带及中部地区;②高石梯地区的天然裂缝长度与裂缝密度呈负指数幂关系,裂缝发育具层间差异性,灰岩储层的缝发育程度高,泥岩对裂缝延伸具阻挡作用;③裂缝发育规模及产状发育受断层、褶皱影响显著,断层周围裂缝密度大、开度大、长度小,剪切缝与走滑断层近于平行或呈低角度,张性缝与主走滑断层呈高角度;褶皱主要通过构造曲率影响裂缝开度,弯曲变形程度高的构造部位裂缝开度大,翼部变形小,裂缝开度小。研究成果可为研究区及其他类似地质条件地区气藏高效勘探开发提供参考与借鉴。

Natural fractures are important storage spaces and seepage channels in tight carbonate reservoirs.It is therefore of practical significance to quantitatively predicting their development and distribution patterns and revealing the dominant geological factors that control the development of gas reservoirs.This study looks at the fractures in the tight carbonate reservoir of Dengying Formation in Gaoshiti block of Leshan-Longnusi ancient uplift in the central Sichuan Basin.Based on the characterization of fracture parameters,we established a calculation model of stress field-energy-fracture parameters,and carried out quantitative prediction of fracture development and distribution patterns by combining multi-phase fracture superimposition algorithms.We then analyzed the influence of lithology,faults,and structural morphology on fracture development.The results show that:(1)The fractures in Dengying Formation of Gaoshiti block are mainly tension-shear fractures,high-angle fractures,and semi-filled fractures.The preferential fracture strike is NW-SE and near N-S directions.The fracture density is between 0 and 2 fractures per meter,and the high-value areas are mainly distributed in the fault zones and central regions;(2)There is a negative exponential power relationship between the length and density of natural fractures in the Gaoshiti block.Fracture development exhibits interlayer differences:The limestone reservoir has a high degree of fracture development,and mudstone has a blocking effect on fracture propagation;(3)Fracture development scale and occurrence are significantly affected by faults and folds:fracture around faults shows high density,large aperture and short length.Shear fractures are nearly parallel or at a low angle to strike-slip faults,and tensile fractures are at a high angle to the main strike-slip faults;folds mainly affect fracture aperture through structural curvature,with larger fracture apertures in high-degree deformation structural positions,and smaller values in the wings.The results could provide references for efficient exploration and profitable development of gas reservoirs in the study area and other regions with similar geological conditions.