用气测资料计算岩石含烃浓度

Calculating the concentration of hydrecarbon gases in rock by mud logging.

岩石含烃浓度是油气勘探中的一项重要参数。文中建立了一套用气测资料计算岩石含烃浓度的理论和方法。地层中天然气常以游离气、吸附气和水溶气３种形式存在。当钻头破碎岩石时，钻井液把这些气体携至井口。通过气测仪获得的气测资料，以及钻时、钻井液排量、井眼尺寸、气测全脱分析和气测仪有关参数等，可计算钻经每米地层所耗钻井液中的天然气体积。岩石含烃浓度（每立方米岩石的含气量）与被钻岩石体积的乘积为所钻岩石中的天然气体积，该体积应与钻井液中所含的天然气体积相等，从而可求得岩石含烃浓度。经储集层段测并解释孔隙度、含气饱和度及天然气膨胀系数等校正，可作出岩石含烃浓度随深度剖面变化的成果图。应用上述方法在川西白马庙地区５口井成功地计算了岩石含烃浓度，为该区的油气生成、运聚、成藏研究和勘探决策等提供了重要的地质依据。图４参８（蔡开平摘）

The concentration of hydrocarbon gases in rock (CHGR) is an important parameter in oil and gas exploration. The theory and method were established herein to calculate CHGR. Hydrocarbon gases in the subsurface exit in free form, by absorbing on organic matter and mineral particles, or by dissolving in formation water. As the drill bit breaks the rock into small cuttings, the gas present is released into the mud stream. As the mud comes out of the hole, a portion is run into a mud-gas separator. The hydrocarbon gas volume (HGV) in the mud depleted to drill 1m layers is calculated from the gas logging data, drilling time, mud displacement, hole size, quantitative gas analysis and instrument's parameters. With C standing for CHGR (cubic meter gas/cubic meter rock), the HGV in the rock drilled 1m footage is equal to the C multiplied by the penetrated rock volume. C is calculated from the equality between the HGV in the rock and the one in the mud. The variation of CHGR with depth is available from the calibration of the porosity, gas saturation of electric log interpretation of the reservoir and hydrocarbon gases expansion coefficient. The calculating 5-well CHGR of Baimamiao area in Western Sichuan basin supplied the important geological basis for hydrocarbon generation, migration, accumulation and exploration decision.