Paleo-oil-Water Contact and Present-Day Gas-Water Contact:Implication for Evolution History of Puguang Gas Field, Sichuan Basin, China

【摘要】 The Puguang (普光) gas field is the largest gas field found in marine carbonate in China. The Puguang gas field experienced complicated evolution history from paleo-oil pool to gas pool. The purpose of this article is to reveal the evolution history of Puguang gas field through systematic study on the relationship between paleo-oil-water contact (POWC) and present-day gas-water contact (PGWC). POWC was recognized by observing the change of relative content of residual solid bitumen in the cores, and PGWC was observed using log and drilling stem test data. Two types of relationship between POWC and PGWC were observed in the Puguang gas field: POWC is above PGWC, and POWC is below PGWC. The former is normal as oil cracking may cause gas-water contact to move downward. The latter can be interpreted by lateral gas re-migration and re-accumulation caused by changes in structural configuration. The relationship between POWC and PGWC suggests that during oil charge, the southwestern and northwestern parts of the Puguang gas field were structurally lower than the northeastern and southeastern parts. Thrusting from Xuefengshan (雪峰山) since Yanshanian movement and from Dabashan (大巴山) since Himalayan movement resulted in the relative uplift of the southwestern and northwestern parts of the Puguang structure, which significantly changed the struc- tural configuration. Based on the paleo-structure discussed in this article, the most probable migration directions of paleo-oil were from the northwest to the southeast and from the southwest to the northeast. Consequently, the evolution history of the Puguang gas field can be divided into three stages, namely,oil charging (200-170 Ma), cracking oil to gas (155-120 Ma), and gas pool adjustment (120-0 Ma).更多还原

【Abstract】 The Puguang (普光) gas field is the largest gas field found in marine carbonate in China. The Puguang gas field experienced complicated evolution history from paleo-oil pool to gas pool. The purpose of this article is to reveal the evolution history of Puguang gas field through systematic study on the relationship between paleo-oil-water contact (POWC) and present-day gas-water contact (PGWC). POWC was recognized by observing the change of relative content of residual solid bitumen in the cores, and PGWC was observed using log and drilling stem test data. Two types of relationship between POWC and PGWC were observed in the Puguang gas field: POWC is above PGWC, and POWC is below PGWC. The former is normal as oil cracking may cause gas-water contact to move downward. The latter can be interpreted by lateral gas re-migration and re-accumulation caused by changes in structural configuration. The relationship between POWC and PGWC suggests that during oil charge, the southwestern and northwestern parts of the Puguang gas field were structurally lower than the northeastern and southeastern parts. Thrusting from Xuefengshan (雪峰山) since Yanshanian movement and from Dabashan (大巴山) since Himalayan movement resulted in the relative uplift of the southwestern and northwestern parts of the Puguang structure, which significantly changed the struc- tural configuration. Based on the paleo-structure discussed in this article, the most probable migration directions of paleo-oil were from the northwest to the southeast and from the southwest to the northeast. Consequently, the evolution history of the Puguang gas field can be divided into three stages, namely,oil charging (200–170 Ma), cracking oil to gas (155–120 Ma), and gas pool adjustment (120–0 Ma).更多还原