深层气层识别方法研究

STUDY ON THE METHOD OF RECOGNIZING DEEP GAS ZONE

常规测井资料识别天然气主要依据的是三孔隙度测井曲线。理论上认为,储层含气使声波时差孔隙度和密度孔隙度增大,使中子孔隙度减少。以此为基础,已发展了一系列有效的方法,但这些方法在东濮凹陷深层气应用中效果明显下降。该区深层气藏类型为低渗透凝析气藏,具有含气饱和度低、凝析油含量高的特点,因此使深层气在探测范围比较浅的三孔隙度测井资料上显示较弱,如何突出天然气在三孔隙度测井曲线上的细微变化是深层气识别的关键。文章以天然气测井响应理论为基础,计算出天然气对三孔隙度测井曲线声波时差、补偿中子、补偿密度不同的影响量,考虑到天然气在孔隙度曲线上的影响变化量的差异及仪器探测深度,提出了用含气当量法来识别深层气,该方法的优点在于其重点突出了天然气对声波时差的影响量,因此识别精度明显改善,在东濮凹陷深层天然气测井解释应用中,识别符合率明显提高,取得了较好的地质应用效果。

Recognizing natural gas with convention log data mainly is based on 3 porosity log curves. It is theoretically considered that reservoir gas-bearing makes interval transit time porosity and density porosity increase and neutron porosity decrease. On this basis, a series of effective methods have been developed. But the application effects of the methods obviously decline in deep gas zones. The deep gas reservoir of Dongpu Sag belongs to low-condensate gas pool with the characteristics of low permeability, low gas-bearing saturation and high condensate content, which makes the deep gas have a weak display of 3 porosity log data of shallow investigation depth. How to display the gas's subtle changes in 3 porosity log curves is the key of deep gas recognition. By gas log response theory, the gas's different influence contents on interval transit time, compensated density in 3 porosity log curves are calculated in this paper. On the basis of considering the differences of gas's influence change contents in porosity curve and the investigation depth of detector's, the gas-bearing content method of recognizing deep gas is proposed out. The merits of the method can emphatically display the gas's influence content on interval transit time. So, the recognition precision is obviously raised, which is proved in the application of deep gas log interpretation in Dongpu Sag.