四川盆地彭州气田三压力剖面计算在复杂预防与处理中的应用

Application of three-pressure profile calculation to complex situation prevent and treatment in Pengzhou Gas Field,the Sichuan Basin

四川盆地彭州气田位于龙门山前构造带,由于地质情况复杂,前期钻井井涌、井漏、掉块、卡钻等复杂情况频发,增加了钻井周期和成本,影响了气田的高效勘探和开发。因此,有必要在计算三压力剖面基础上,找出复杂情况发生原因,为预防与处理复杂情况提供科学依据。通过优选伊顿法计算地层孔隙压力、库仑—摩尔强度准则计算地层坍塌压力、最大拉应力理论计算地层破裂压力等方法,建立地区三压力剖面。在此基础上,通过对三压力剖面、岩性、掉块形态、井径曲线等资料分析,弄清了复杂情况发生的原因。研究发现井涌是钻遇高压气层时钻井液密度过小,在压井过程中使用过高钻井液密度压破上部疏松地层;井壁掉块是因地层微裂缝发育,高密度钻井液易滤失沿微裂缝渗透进入地层,增大坍塌压力导致井壁失稳;四开卡钻是因马一段发育的页岩掉块卡入取心钻头和井壁。通过采取优化井身结构和改善钻井液防塌性能和封堵性确定合理钻井液密度等措施,钻井复杂情况减少59.5%,钻井周期减小29.8%,钻井提速显著、节约了钻井成本。

Pengzhou Gas Field of the Sichuan Basin is located in Longmen piedmont tectonic belt. It is geologically complex, so com- plex downhole situations occur frequently in the early drilling stage, such as well kick, lost circulation, falling and pipe sticking. As a result, the drilling cycle and cost are increased, and the efficient exploration and development of Pengzhou Gas Field is impacted. Therefore, it is necessary to find out the causes of the complex situations by calculating three-pressure profile, so as to provide the scientific basis for preventing and dealing with the complex situations. In this paper, the three-pressure profile of this area was estab- lished by taking the method of Eaton to calculate the formation porosity pressure, the Coulomb-Mohr strength criterion to calculate the formation collapse pressure, and the maximum tensile stress theory to calculate formation fracture pressure. Then, three-pressure pro- file, lithology, falling morphology and caliper log were analyzed to find out the causes of complex situations. The following research results were obtained. First, the reasons for well kick are that the density of drilling fluid to drill high pressure gas layers is too low and the upper unconsolidated formation is fractured when the density of drilling fluid used in the process of well killing is too high. Second, the micro-fractures in the formation are developed, so high-density drilling fluid tends to leak off and flows into the formation along the micro-fractures, increasing the collapse pressure. As a result, the borehole wall gets instable and drops. And third, the reason for the pipe sticking in the fourth section is that shale fallings developed in Ma 1 Member are stuck in coring bit and borehole wall. After a series of measures are taken, such as optimizing casing program, improving the anti-collapse performance and plugging capac- ity of drilling fluid, and determining rational density of drilling fluid, the complex drilling situations are decreased by 59.5%, drilling cycle is shortened by 29.8%, rate of penetration is increased significantly and drilling cost is cut down.