Study On The Development Law And Technical Policy Optimization Of Horizontal Wells In Ultra-low Permeability Reservoirs

In this paper,the QM oilfield YM ultra-low permeability reservoirs are taken as typical examples to study the development law and main control factors of horizontal wells in ultra-low permeability reservoirs.Firstly,the dynamic analysis and field statistics method are used to analyze the variation of horizontal well productivity,water cut,and production decline in YM area,and evaluate the development effect of horizontal wells;The water injection effect in the study area is evaluated through the analysis of the water driving degree,the analysis of the pressure variation law and the calculation of the water drive efficiency.The different development characteristics of short five point method,seven point method and nine point well pattern are compared and analyzed;According to the effect of horizontal well,the productivity of horizontal well is classified,and the productivity,water cut,pressure and decreasing change are compared and analyzed.Secondly,by comprehensively applying the reservoir engineering,numerical simulation and mine site method,the influence factors of horizontal well productivity were analyzed and the influence laws were studied from the following three aspects:geological factors,well network factors and horizontal well rehabilitation parameters;In the low-yield and low-efficiency wells in the study area,combined with macro factors and micro-mechanisms,the causes of low production in horizontal wells,causes of water seepage,and causes of decline were analyzed.Finally,a numerical model is established to simulate the horizontal well pattern parameters and injection-production technical policy index of ultra-low permeability reservoir,and the reasonable parameters and technical indexes are optimized.The results show that the horizontal well development effect is not good,the high-yield wells are decreasing,and wells with high water cut are increasing;the water injection effect is poor,and the formation energy is insufficient.The production decline rate is fast in the early stage,mostly consistent with exponential decline and hyperbolic decline,and the decline rate of production in the middle and late stage of production is gentle,and most of them accord with harmonic decline.With low injection-production ratio and high productivity,five-spot well pattern has better adaptability in ultra-low permeability reservoirs.The productivity of horizontal wells is positively correlated with reservoir thickness,permeability,horizontal segment length,fracture density and fracturing fluid volume,but the increase of productivity is decreasing.Horizontal wells with low production and low efficiency are affected by macro factors such as reservoir physical properties,degree of transformation,water injection policy,etc.,and controlled by macroscopical factors such as liquid resistance effect,wetting hysteresis,etc.The optimization results of the YM area parameters:the horizontal well length under the five-point well network is 500m,the well spacing range is 400-500m,the row distance is 120m,the fracture density is 1.9 sections/100m,and the length of the joint is 160m~110m.Good water injection timing is ahead of 3 months,water injection volume is 1100-1130m3,single well daily water injection volume is 16 m~3;reasonable bottomhole flow pressure is 6.2-6.6MPa,oil recovery rate is 0.8%,injection and production ratio is 1.2:1.