Biogas Losses In Its Accumulation In The Bohaiwan Basin

Biogas losses contol its distribution and accumulation, but biogas losses are less studied. There are many different genetic types of biogas in Bohaiwan Basin, and their charging and loss are complex. Analysis the loss ways of different genetic types of biogases and evaluate the loss behavior quantitatively help to understand the control factors of biogas accumulation.Take typical biogas reservoirs in Bohaiwan basin as examples, as guild of geochemical and natural gas geology, base on the geochemical characteristics of biogases, the genetic types of biogases in Bohaiwan Basin are divided, and the accumulation characteristics of biogas are studied. The genetic types of biogas in Bohaiwan Basins can be divided into primary-buired biogas, secondary buried biogas and oil-degradation biogas. Immature source rocks which riched in organic matters are material basis and loss control the accumulation of primary buried biogases. Source rocks back to microbial zone and surface water intrusion is the key facters for secondary buried biogas foramtion. Surface water intrusion and interaction with cruid oil control the formation of oil-degraded biogas. Fault controls the accumulation and hydrocarbon loss process of both secondary buried biogases and oil-degraded biogases.As the guide of kinetic theory of gas accumulation and hydrocarbon migration theory, take Yangxin Es1 primary biogas, Liuquan Es3 secondary biogas and Shanjiasi N oil-degraded biogas as examples, biogas loss processes are studied, and hydrocarbon losses geological models and mathematic models are established. Evaluation results show that: Leakage along the capcock or transport layer and diffusion are main loss ways of primary buried biogas. Leakage by caprock has a huge destructive effect on biogas reservoirs, and the loss rate can reached 10^-310^-1m³/s, it can make an industrial gas reservoir completely depleted in a short time. Leakage by transport layer control the biogas accumulation effectively, and loss rate of it is about 10^-410^-3m³/s. Diffusion play less important roles in biogas losses, but always impact vertical distribution of biogas. Biogas lost by fault associated crack with episodic pressure pipe flow during faulting period, and lost by derived fracture with Darcy leakage during fault resting stage, the loss rate of later is far below former. With the increase of depth, because of compaction and cementation, the porosity and permeability of derived fracture decrease, and the loss rate decreased. It indicates that the biogas reservoirs which controlled by fault are more likely to be accumulated in later stage.