川西坳陷须家河组二段气藏地震相特征研究

Seismic facies of gas reservoir within the second member of Xujiahe formation in west Sichuan depression

(1.成都理工大学“油气藏地质及开发工程”国家重点实验室，四川成都610059；2.中国石油化工股份有限公司西南分公司勘探开发研究院德阳分院，四川德阳618000)

The gas reservoir of Xujiahe formation is characterized by great buried depth, super-tight sand bodies with strong anisotropy. The analysis on reservoir shows that the pores are mainly generated by denudation and developed in sand bodies of mouth bar facies. The mature degree of the sand bodies containing much feldspar is relatively low. The mouth bar contacts with the frontal sand bar and acidic water can easily flow into mouth bar. The feldspar in sand bodies of mouth bar is dissolved and generates secondary pores. So, the oil/gas concentration model is built as that 1) during hydrocarbon generation period, taking the fault as passageway and thick delta front sand bodies as dredging layer, acidic water flows into mouth bar and denudates in feldspar-porphyry sandstone, and 2) oil and gas enter mouth bar and form hydrocarbon accumulation zone at the early stage. The prediction of potential sedimentary belt in mouth bar is the key of gas reservoir exploration in Xujiahe formation. The typical X851 well was used to establish the sand bodies of mouth bar facies and the prediction mode of hydrocarbon accumulation belt. The results show that the sand bodies of mouth bar facies displays typical S-shaped reflection configuration on longitudinal profile, shell-like reflection configuration on cross section, and horseshoe distribution on plane. The characteristics of seismic facies were utilized to predict the potential reservoirs and hydrocarbon accumulation belts in Xinchang gas field, with the result in good accord with the drilling data.

川西坳陷须家河组二段气藏埋深大，砂体超致密、非均质性强。砂体物性特征分析表明，优质储层的孔隙主要由溶蚀作用形成，且大都发育在河口坝砂体中。河口坝砂体成熟度相对较低，含有相对较多的长石。河口坝与前缘砂坝接触，酸性水容易进入河口坝，河口坝砂体中的长石受酸性水溶蚀，形成次生孔隙。由此建立油气富集模式：生烃时期，以断层为通道、厚大的前缘相砂体为疏导层，酸性水进入河口坝砂体，在长石砂岩中发生溶蚀作用，油气早期进入河口坝砂体，形成早期油气富集带。通过分析典型的X851井，建立河口坝砂体、油气富集带预测模式：河口坝在纵剖面上具有典型S型前积反射结构，横切面呈贝壳形丘状反射，平面呈马蹄形分布。用地震相特征预测了新场气田优质储层、油气富集带分布，结果与钻井吻合。

State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Chengdu University of Technology, Chengdu 610059, China