深盆气成藏平衡原理及数学描述

Equilibrium Principle and Mathematic Description for Source-Contacting Gas Accumulation

天然气从底部向储层中的注入过程一般可分为两种典型特征,一种是具有通常意义的置换式运移和成藏,形成常规气藏;另一种是具有活塞式气水排驱特征的天然气运移和成藏,形成天然气聚集与气源岩紧密相连的深盆气(根缘气)藏。深盆气藏形成的基本条件是储层致密、源储相通,但当致密储层中有裂缝发育时,典型的深盆气成藏条件不再满足,气水的排驱过程表现为置换式和活塞式的同时存在和发生。对典型和复杂情况下的深盆气成藏条件进行了讨论,分别建立了成藏时相应的动力平衡方程,对所建立方程的应用也进行了相应讨论。结果表明,深盆气成藏的基本条件是气源丰富、储层致密、源储相通、储盖一体。除此之外,埋藏深度和时间变化是典型深盆气藏的重要影响因素。

The driving of water by natural gas in tight sands is an extremely a complicated process. The injecting of gas from the bottom of tight sands has the feature of piston-fashioned water driving when both porosity and permeability of the sands are homogeneous. The accumulation of gas will be typically source-contacting or root-sourced when the driving of water by gas is piston-fashioned. Typically, source-contacting gas or basin-centered gas will not be accumulated when the tight sands are of heterogeneous or even fractured, since the piston-typed and replacement-fashioned driving of gas will occurr in the same time. In this paper, we will discuss the accumulation conditions and equilibriums of source-contacting gas for typical and practical hypothesis. Conditions for the accumulation of source-contacting gases or rooting gases can be summarized into the regional existence of tight sands, abundant supplying of generated gas, directly contact between source rocks and reservoirs, and integration of reservoirs and seal rocks. As a result, the equilibrium equations for the formation of different types of source-contacting gases, or basin-centered gases are established respectively. Further more, the applications of equations is concisely discussed. The result indicates that the formation condition of typical source-contacting gas is not related to the height of gas column as in normal gas accumulation, instead, it is closely related to the buried depth.