水驱气藏气相阈压梯度预测模型

鉴于现有气相阈压梯度预测模型不能准确描述气相阈压梯度随气相连续性的变化规律,在改进气相阈压梯度实验流程的基础上,选取四川盆地普光气田下三叠统飞仙关组碳酸盐岩储层标准岩心,开展了气相阈压梯度实验,建立了综合考虑岩石渗透率和气相连续性的气相阈压梯度预测模型,对比分析了基于不同气相连续性表征参数建立的气相阈压梯度预测模型的预测结果。然后,根据该气藏气井的测井解释成果,采用基于相对可动气饱和度建立的气相阈压梯度预测模型,预测了不同类型储层的气相阈压梯度。研究结果表明:①相对可动气饱和度考虑了束缚水饱和度和残余气饱和度对气相连续性的影响,较之于含水饱和度而言,相对可动气饱和度能够更好地表征气相在多孔介质中的连续性;②气相阈压梯度随岩石渗透率、相对可动气饱和度的降低而增大,在渗透率、相对可动气饱和度较低时,气相阈压梯度随渗透率、相对可动气饱和度的降低而急剧增大;③普光气田主体气藏Ⅰ类储层的气相阈压梯度较小,其数量级在0.01 MPa/m,Ⅱ类储层的气相阈压梯度较Ⅰ类储层有所增大,Ⅲ类储层的气相阈压梯度则急剧增大。结论认为,基于相对可动气饱和度建立的气相阈压梯度预测模型能够更加准确地描述气相阈压梯度随岩石渗透率和气相连续性的变化规律,所取得的研究成果可以为准确认识水驱气藏气—水两相渗流规律奠定基础。

A prediction model for the gas threshold pressure gradients of water drive gas reservoirs

The existing prediction models for gas threshold pressure gradients can not accurately describe the variation of gas threshold pressure gradients with gas continuity. In order to solve this problem, this paper improved the experimental process of gas threshold pressure gradients. Based on this, the standard cores of a carbonate reservoir of Lower Triassic Feixianguan Formation in the Puguang Gas Field of the Sichuan Basin were selected for the experiment of gas threshold pressure gradients. Then, a new model for predicting the gas threshold pressure gradients while taking into consideration the rock permeability and gas continuity comprehensively was established, and the prediction results of the gas threshold pressure gradient predicting models established based on different gas continuity characterization parameters were compared and analyzed. Finally, based on the logging interpretation results of the gas wells in this reservoir, the gas threshold pressure gradients of different types of reservoirs were predicted using the gas threshold pressure gradient predicting model established on the basis of relative movable gas saturation. And the following research results were obtained. First, the relative movable gas saturation takes into consideration the influence of irreducible water saturation and residual gas saturation on gas continuity, and compared with water saturation, it can describe the gas continuity in porous media more accurately. Second, gas threshold pressure gradients increase with the decrease of rock permeability or relative movable gas saturation, and when permeability or relative movable gas saturation is lower, they rise sharply with the decrease of permeability or relative movable gas saturation. Third, the gas threshold pressure gradients of type I reservoirs in the main gas reservoirs of the Puguang Gas Field are lower with a magnitude order of 0.01 MPa/m. The gas threshold pressure gradients of type Ⅱ reservoirs are higher than those of type Ⅰ reservoirs, while the gas threshold gradients of type Ⅲ reservoirs rise sharply. In conclusion, the gas threshold pressure gradient predicting model established based on relative movable gas saturation can describe more accurately the variation laws of gas threshold pressure gradients with rock permeability and gas continuity. These research results lay a foundation for the correct understanding of the seepage laws of the gas–water two-phase flow in water drive gas reservoirs.