Natural Gas Origins of the Large--Medium Sized Gas Fields in China

Dai Jinxing, Xianqi Li, and Shengfei Qin

Large-medium sized gas field refers to the gas field with proved reserves over 100 × 10⁸m³. By the end of 1994, 30 large or medium sized gas fields have been found in China (except for Taiwan province), of which the proved gas reserves account for 71% of the total chinese gas reserves. And four origins of the natural gases of large-medium sized gas fields have been determined in China: (1) Oil-type gas holds a dominant position of the gases, is primarily dry with ^dgr¹³C₁ values ranging from -- 39.82^pmil to -- 31.93^pmil, R/Ra ratio values being 0.003~0.150; (2) Coal--formed gas takes the second place of the gases, is predominately wet gas, with ^dgr¹³C₁ values from -- 39.55^pmil to -- 27.80^pmil, and R/Ra ratio values of 0.016~0.686; (3) Mixed-gas is mainly dry gas, with ^dgr¹³C₁ values varying within -- 35.87^pmil~--33.40^pmil, R/Ra ratio values being 0.014~0.040; (4) Biogenic gas is only dry gas, with ^dgr¹³C₁ values from -- 68.54^pmil to -- 64.90^pmil, R/Ra ratio values of 0.030~0.305. In a word, this paper elaborates the natural gas origins of chinese large-medium sized gas fields, based on the full and accurate data of gas components, carbon isotopic compositions of alkane gases (^dgr¹³C_1~4) and Carbon dioxide (^dgr¹³C_CO2), and the associated helium isotopes (R/Ra).

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California