中牟区块过渡相页岩气藏产能分析及压裂参数优选

Production analysis and fracturing parameter optimization of shale gas from Zhongmou Block in southern North China Basin

南华北盆地中牟区块页岩气是海陆过渡相页岩气的典型代表,以地质模型为基础,结合理论分析和数值模拟手段,研究了不同储层参数对水平井开采页岩气的采收率、日产气量以及累计产气量的影响规律,通过正交设计与多指标分析方法确定了影响页岩气产能的主控因素,考虑各主控因素与页岩气产能的关系,建立了水平井压裂条件下的累计产气量和页岩气采收率方程.针对目标压裂层段,对比分析了不同压裂参数条件下的页岩气产能变化,指出水平井段长度和动用程度是决定产能大小的主要参数.在一定的压裂级数条件下,裂缝长度的增加可以有效沟通裂缝,从而提高产能.以净现值大于0和收益率达到8%~12%作为经济评价指标,优选了3类海陆过渡相页岩气压裂参数.

Shale gas is a type of unconventional natural gas that can be accumulated in a large area in tight shale and has selfgeneration and self-storage abilities.The low porosity and low permeability characteristics of shale make its development under natural conditions poor,and large-scale stimulations of its production are needed to achieve economic benefits.Due to the complex geological tectonic conditions in China,three types of organic-rich shale strata,namely,marine facies,marine-continental facies,and continental facies,are developed during the multicycle tectonic evolution.China has made important breakthroughs in the exploration and development of marine shale gas.Considerable effort has also been invested in the exploration of continental shale gas.The exploration and research of marine-continental transitional shale have gradually attracted people’s attention.Marine-continental transitional shales are of importance to the shale gas field.However,research on transitional shale gas exploitation is still in its infancy,and this topic needs to be urgently discussed and solved.Shale gas exploitation seriously restricts the development level of shale gas in China.The shale gas in the Zhongmou Block of the southern North China Basin is a typical representative of marine-continental transitional shale gas,with good gas resources and development prospects.In this study,based on a geologic model,the influences of different reservoir parameters on oil recovery,daily gas production,and cumulative gas production were examined through the integration of theoretical analyses and numerical simulations.The main factors affecting the gas production capacity of shale were determined by an orthogonal design and multi-index analysis.Considering the relationship between main control factors and shale gas production capacity,the cumulative gas production and shale gas recovery equations under the horizontal fracturing condition were established.For the target fracturing zones,the shale gas productions under different fracturing parameters were compared and analyzed,which shows that the horizontal length and producing degree are the main parameters that determine the production capacity.In a certain fracturing condition,the increase in fracture length can effectively communicate natural cracks,thereby increasing production capacity.Taking a net present value greater than 0 and a yield rate ranging from 8% to 12% as the economic evaluation indices,three types of fracturing parameters are optimized for the marine-continental transitional shales.