Reservoir-forming conditions and key exploration & development techniques for Xushen gas field in Northeast China

Abstract

Exploration and development of volcanic gas reservoirs is a world-class problem, and less experience can be learned at home and abroad. Through study of reservoir-forming conditions of Xushen gas field, four sets of hydrocarbon source rocks, mainly mudstone and coal seam of Shahezi Formation, are identified in this gas field; its cap rocks are mudstone in Member 2 of Denglouku Formation, and Member 1 and Member 2 of Quantou Formation. By simulating reservoir-forming history, four filling periods of the Xushen gas field are determined, and the most favorable exploration targets are crater areas with structural highs, large thickness and good physical properties. On the basis of diagenetic mechanism study, the criteria of sequence series, lithology identification and reservoir types of gas reservoirs have been established; the volcanic rock bodies have been carefully depicted and the distribution laws of effective reservoirs of gas pools have been figured out. Based on evaluating reservoir-permeability characteristics of reservoirs, the gas well productivity characteristics (mainly type II, III and IV wells) have been identified, and the optimum design technology for volcanic gas reservoir development has been developed. The gas reservoirs in all blocks of Xushen gas field are classified into three types: single-body gas reservoir model, disconnected multi-body gas reservoir model and interconnected multi-body gas reservoir model. Stimulation technologies, including multi-layer fracturing of vertical well, staged fracturing of open-hole horizontal well and volume fracturing, have been developed. According to gas well production performance, pressure change, well-controlled reserves and spatial distribution of volcanic bodies, combined with numerical simulation and prediction of gas reservoirs, the evaluation method of residual potential of volcanic gas reservoirs has been formed. Key technologies for effective exploration and development of complex volcanic gas reservoirs have been established and perfected, and bring good development effect. The research results can provide guidance and reference for exploration and development of similar gas reservoirs. Keywords: Xushen gas field, Reservoir–forming conditions, Volcanic rock, Development, Productivity, Optimum design