海上埕岛油田低渗透油藏压裂井产能模型研究

Study on Productivity Model of Low Permeable Reservoir Vertical Fracture Well of Chengdao Offshore Oilfield

低渗透油藏具有应力敏感性强、启动压力梯度等非线性渗流特征,对油井产能的预测也因此变得十分困难。综合考虑储层裂缝发育、应力敏感性、启动压力梯度以及流体的微可压缩性等因素,运用非线性渗流理论,建立了低渗透油藏垂直裂缝井的非线性稳定渗流模型,运用保角变换得到模型的解析解。结合埕岛油田埕北32东营组低渗透油藏开发实例,研究结果表明:油井产能随裂缝半长的增大而增加,随应力敏感系数的增大而降低。在生产压差小于2 MPa时,裂缝半长和应力敏感系数对产能的影响并不明显;采油指数随着生产压差的增加出现大幅下降。当生产压差超过2 MPa,裂缝半长和应力敏感系数的影响将变得十分显著,裂缝半长增大到6倍,油井产能相应增加为2.5倍,应力敏感系数增大到10倍,油井产能相应下降为1/2;而采油指数的下降将变得比较平缓,直至最后趋于稳定或略有上升的趋势。对CB32A-3、CB32A-4两口压裂井产能进行预测,预测误差在10%以内,测算结果具有较高的精度。

The existences of stress sensitivity and threshold pressure gradient in low permeable reservoirs lead to its complex characteristics of nonlinear seepage flow. And the prediction of oil well productivity also becomes quite difficult. Based on the consideration of fracture development, the micro-compressibility of Newton fluid, the stress sensitivity of permeability and threshold pressure gradient, using the nonlinear seepage theory, the model of nonlinear stable seepage of vertical fracture well is established, the analytic solution of the model is derived through conformal mapping. Take the development of low permeable reservoir of block Chengbei 32 Dongying formation in Chengdao oil-field as an example, the results show that the productivity increases with the increase of fracture length, and decrea- ses along with the increase of stress sensitive coefficient. When production pressure difference is less than 2 MPa, the influence of fracture length and stress sensitivity coefficient to productivity is not obvious, while the productivity index showed a sharp decline as the increase of production pressure difference. When production pressure difference is bigger more than 2 MPa, the influence of fracture length and stress sensitive coefficient will become significant. If the fracture length adds up to 6 times, the productivity will increase to 2. 5 times, the stress sensitive coefficient increases to 10 times, corresponding the productivity will reduce to 1/2. While the decline scope of productivity index will become quite gentle, finally tends to be stable or slightly rising. The model is also applied to forecast the productivity of wells CB32A-3-4, the calculation percentage error is within 10%, the results are of highly accurate.