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

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:singlebody 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.

Fine Stratigraphic Division of Volcanic Reservoir by Uniting of Well Data and Seismic Data—Taking Volcanic Reservoir of Member One of Yingcheng Formation in Xudong Area of Songliao Basin for an Example

Taking member one of Yingcheng Formation of Cretaceous in Xudong area, Xushen Gas Field of Songliao Basin for an example and aimed at the diachronous problem generally existed in vol- canic reservoir division, firstly advanced the method of two steps and two unites in the researches of volcanic reservoir finely division that guided by the method that sources controlled and founded the stratigraphic trellis. In this process, volcanic edifices and bodies were identified and traced. The results indicated that aimed strata in study areas could be carved up to six layers of YCII1, YCII2, YCII-II, YCIIlI, YCIII2 and YCIIII from the top to the bottom. Analyzing causes and firmly united of well data and seismic data could achieve fine stratigraphic division of volcanic reservoir. Surfaces of layers and volcanic bodies were basically unanimous in side direction. Stratum inclination gradually reduced with the distances increased from craters. The results of volcanic reservoir division had preferable con- sistency with lithologies and volcanic lithofacies and dynamic development data. The researches offered a useful method to stratigraphic division of volcanic reservoir and it had very important significance to effective development of volcanic reservoir in practice.