川中地区加里东末期洗象池组岩溶储层发育模式及其油气勘探意义

四川盆地寒武系洗象池组钻井过程中油气显示丰富，是盆地内的后备勘探领域和重要接替层系，但目前该层系的勘探程度较低、对优质储层的分布规律认识不够深入。为了确定川中地区洗象池组下一步的天然气勘探方向和目标，利用典型露头、岩心、薄片观察等资料，采用井震结合的方法，研究了其储层特征和岩溶不整合面分布，建立了该区加里东末期洗象池组岩溶储层发育模式，并预测了滩相岩溶储层的有利发育区。研究结果表明：①洗象池组储层岩性以颗粒云岩、晶粒云岩为主，储集空间主要有溶蚀孔洞、粒间孔、晶间孔与裂缝，平均孔隙度为3.46%，平均渗透率为0.99 mD，为低孔低渗裂缝—孔隙型储层；②川中地区洗象池组存在着一条中部宽、南北两侧窄的环状地层剥蚀带，剥蚀带宽度介于6～50 km，面积为4 700 km2；③剥蚀带发育区受加里东末期地层抬升剥蚀的影响，洗象池组发生强烈的风化壳岩溶作用，发育两种类型岩溶储层，其中暴露剥蚀区发育滩相叠加表生岩溶型储层，埋藏区发育滩相叠加顺层岩溶型储层；④西充—广安—潼南地区为滩相岩溶储层最为有利的发育区，面积为5 000 km2。结论认为，西充—广安地区毗邻下寒武统筇竹寺组生烃中心，通源断裂发育，洗象池组滩体规模大、岩溶作用强，易形成滩相叠加加里东末期岩溶作用的规模有效储集体，可作为洗象池组下一步天然气勘探的有利目标。

Development models of Xixiangchi Formation karst reservoirs in the Late Caledonian in the central Sichuan Basin and its oil-gas exploration implications

Oil and gas shows are abundant in the process of drilling the Cambrian Xixiangchi Formation in the Sichuan Basin, so this formation is the reserve exploration area and the important replacement formation in this basin. At present, however, it is less explored and the distribution laws of its high-quality reservoirs are not understood sufficiently. In order to determine the next natural gas exploration directions and targets of Xixiangchi Formation in the central Sichuan Basin, this paper studied its reservoir characteristics and the distribution of karst unconformity using the well-seismic combination method, based on observation data of typical field outcrops, cores and thin sections. Then, a development model of the Xixiangchi Formation karst reservoirs in the late Caledonian in this area was established, and the favorable development area of shoal-facies karst reservoir was predicted. And the following results were obtained. First, the Xixiangchi Formation reservoir is lithologically composed of grain dolomite and crystalline dolomite. The reservoir space is dominated by dissolved pores, intergranular pores, intercrystalline pores and fractures. It is a low porosity and low permeability fractured-porous reservoir with an average porosity of 3.46% and an average permeability of 0.99 mD. Second, in the Xixiangchi Formation, there is a ring-shaped denudation zone that is wide in the central part and narrow in the southern and northern sides, and 6-50 km in width and 4 700 km2 in area. Third, due to formation uplifting and denudation in the development area of denudation zone in the Late Caledonian, strong weathering crust karstification occurred in the Xixiangchi Formation, and two types of reservoirs were developed, including the shoal-facies superimposed supergene karst reservoir in the exposed denudation area and the shoal-facies superimposed bedding karst reservoir in the buried area. Fourth, the Xichong-Guang'an-Tongnan area is the most favorable area for the development of shoal-facies karst reservoir, covering an area of 5 000 km2. In conclusion, Xichong-Guang'an area is adjacent to the hydrocarbon generating center of Lower Cambrian Qiongzhusi Formation. In this area, hydrocarbon source faulting is developed, and the Xixiangchi Formation has large shoal bodies and strong karstification, so a large-scale effective reservoir of shoal facies superimposed Late Caledonian karstification tends to form. Therefore, it can be taken as a favorable target of natural gas exploration in the Xixiangchi Formation in the next step.