Volcanic Massif Identification And Study On Distributery Rules Of Fractured Reservoir In Changling No.1 Gas Field

Changling No.1 gas field is located in the central uplift zone of Changling depression, which was structure controlled, multiphase volcanic rock superimposed, and fractured bottom water drive type gas reservoir. Fractured reservoir is characterized by quick lithofacies changes and high heterogeneity. Early seismic studies were focused on identification of volcanic structure; fracture studies were mainly descriptive; and drillings were designed to target at highs of volcanic bodies. Regularity studies, however, have never been done systematically on identification of volcanic massifs, lithofacies classification, and fractured reservoir distribution. Thus, exploration and appraisal in deeper formations and efficient development of the gas field has been restrained.Proceeding from the current status of volcanic reservoir studies, through systematic study on volcanic resevoir identification and prediction technology and methodology worldwide, and integrating state-of-the-art methodologies and instruments of multi-discipline, this paper starting from well log analysis, core description and geostatistic analysis, it systematically summarizes fracture development characteristics of single well phase of Changling No. 1 volcanic body. According to their different geophysical responses, different phases of volcanic activities are classified and detailed descriptions of facture distribution characteristics are presented. Meanwhile, preserved amplitude pre-stack processing method is adopted to obtain series of fracture attribute data; The anisotropy characteristics of seismic attributes, combined with single well phase study result, is used to identifies fracture development intensity and area of volcanic massifs. Main study results of this paper are as follows:1) Basing on previous studies by orher people, this paper define Changling volcanic into three phase further and systematically identifies fracture density and direction of volcanic bodies of each phase. Three sub-phases in the 3rd phase volcanic massif were defined, and systematically analyses the distribution characteristics, area and fracture characteristics of each sub-phase. Among the three sub-phases, CS1-1 volcanic massif has the biggest distribution area and is the most favorable gas-bearing reservor. 2) Two main stress fields, SN and EW, are extrapolated from dominting effect of fracture system to the spatial distribution of fractures. Dual factors of both stress fields and fractures have controlled fracture directions and density. This paper presents macrocharacteristics of lateral and regional distribution of fractures in Changling gas field.3) Main body area of explosive facies and eruptive facies are identified, their lithofacies distribution area restricts the distribution of favorable reservoirs (autobreccited lava), which presents a discontinuous annalur distribution in the center of the study area.This understanding offers theoretical-geologic basis for gas-bearing area prediction. 5 fracture fairways were defined and proposed to drill multi-lateral horizontal wells to develop the gas reservoir, to penetrate as many fracture zones as possible. The study result has been validated by gas production wells.This paper’s study philosophy, methodology, technical process and results provide very important instructions to exploration and development of Changling No.1 fractured gas field and offer a good reference to the development of similar gas fields as well.