南缘超高压致密气藏应力敏感及钻井液污染研究

A Study on Stress Sensitivity and Drilling Fluid Pollution in Ultra-high Pressure Tight Gas Reservoirs in the Southern Margin

储层低渗特征和钻井液污染是影响低渗气藏有效建产的主要因素。基于耐超高温高压实验系统和CT扫描技术研究了新疆油田南缘区块1个高温超高压致密气藏(158.6℃,146 MPa)渗透率应力敏感性以及钻井液污染特征。研究结果表明,1)储层岩芯孔隙中90%以上为粒间孔,且少量粒间孔被方解石胶结物和沥青全充填半充填;2)在净应力110 MPa下,所考察的两块柱塞岩芯(0.0019 mD,0.0325 mD)的应力敏感渗透率降低率(相对于储层实际净应力下)分别为39.28%和16.04%,属于中等偏弱和弱敏感;3)定性和定量表征了另外两柱塞块岩芯(0.0042 mD,0.0290 mD)在实际操作工况下钻井液侵入特征,发现钻井液均没有突破两块岩芯长度,侵入渗透率为0.0290 mD岩芯的深度为3.86 cm,但引起的表皮系数达到6.54,表现为严重污染。研究成果对于掌握高温超高压气藏储层特征、钻井液污染认识以及后续储层保护措施建立提供了重要技术支持。

The low permeability characteristics and the contamination of drilling fluid are the main factors affecting the effective production of low permeability gas reservoirs.Based on the ultra-high temperature and high pressure resistance experimental system and CT scanning technology,the permeability stress sensitivity and drilling fluid pollution characteristics of a high temperature ultra high pressure tight gas reservoir(158.6℃,146 MPa)in the southern margin of Xinjiang Oilfield were studied.The research results show that:1)more than 90%pores in the reservoir cores are intergranular pores,and a small amount of intergranular pores are fully or half-filled by calcite cement and asphalt;2)under the net stress of 110 MPa,the stress-sensitive permeability reduction ratio(relative to the net stress of the initial reservoir)of the two plug cores(0.0019 mD,0.0325 mD)were equal to 39.28%and 16.04%,respectively,which are moderately weak and weak sensitive,respectively;3)qualitatively and quantitatively characterizing the drilling fluid invasion characteristics of the other two plunger cores(0.0042 mD,0.029 mD)under actual operating conditions,it was found that the drilling fluid did not break through the length of the two cores.It was tested that the drilling fluid invasion length in the 0.029 mD core was 3.86 cm,but the skin coefficient caused by it reached 6.54,which belonged to serious pollution degree.The research results provide important technical support for mastering the characteristics of high temperature and ultra-high pressure gas reservoirs,understanding of drilling fluid pollution,and for establishing subsequent reservoir protection measures.