南堡滩海深层天然气藏保护储层钻井液体系研究与效果评价

Development and Application of Drilling Fluid System for Reservoir Protection of Deep Gas Reservoir in Nanpu Offshore Area

南堡滩海是渤海湾盆地北部的一个小型陆相断陷滩海,天然气资源丰富。但因地质条件复杂,储层伤害机理认识不清增加了储层保护难度,同一层位邻井有高产井有失利井,产气量差异显著。通过对比测定不同流体驱替、污染前后的气相及油相渗透率恢复值,分析得出天然气储层的水锁伤害程度较油层高出30~50个百分点。在此基础上利用反渗透及防水锁协同作用理论完善研究了180℃抗高温聚束型低自由水钻井液,体系高温高压失水为8 m L,膜效率可以从0.11提高至0.5,对地层岩心气体渗透率恢复值达到91%。在NPAX-C等两口井上应用,表现出良好的泥页岩抑制性及致密天然气储层保护效果,能够满足利用水基钻井液钻探南堡滩海致密天然气储层的需求。研究成果为南堡滩海致密天然气藏高效勘探提供了更加可靠的技术支持,其技术思路也为国内类似致密天然气藏的勘探开发提供了良好的方法借鉴和示范作用。

Offshore area of Nanpu Sag is a small continental fault depression located at northern Bohai Bay Basin,with rich oil and gas resources.The reservoir protection is rather difficult due to the complicated geological conditions and the poor understanding to the mechanism of reservoir damage in this area,which results in the occurrence of high-yield well or dry well within a small range with the same target layers,and with the similar situation in the gas production.The comparison and analysis of the recovered gas and oil permeability of core samples measured pre-and post-displacement with different fluids indicate that the water blocking damage in the gas reservoir is30~50percent higher than that of oil reservoir.On the basis of that,180℃high temperature polymeric micelle drilling fluid was developed under the guidance of reverse osmosis and water-lock prevention theory.Experimental results show that the membrane efficiency of the drilling fluid increases from0.11to0.5,and the gas permeability recovery of core sample reaches91%.The application of the drilling fluid in Well NPAX-C and another well shows that the drilling fluid can meet the needs of drilling the tight gas reservoir with water-based drilling fluid in Nanpu offshore area due to its perfect shale inhibition and gas reservoir protection performance.This study provides more reliable technical support to the efficient exploration of the tight gas reservoir in Nanpu Sag,and the technical thinking also can provide valuable reference and demonstrative effect on the exploration and development of the other areas with the similar tight gas reservoir.