The deeply buried shoal dolomite reservoirs of the Lower Triassic Feixianguan Formation, giant Puguang Gas Field, NE Sichuan Basin, are exceptionally porous. The influences of diageneses on pore evolution are studied....The deeply buried shoal dolomite reservoirs of the Lower Triassic Feixianguan Formation, giant Puguang Gas Field, NE Sichuan Basin, are exceptionally porous. The influences of diageneses on pore evolution are studied. Through petrologic investigation, diagenetic phases are divided into four stages, i.e., near-surface, pre-oil window, oil window, and gas window. The Adobe Photoshop system is used to quantify the rock texture components, porosity constitutions and the influences of diageneses on reservoir porosity. Porosity evolution curves are quantitatively recovered. The Feixianguan reservoir porosities are mainly created by early meteoric dissolution, dolomitization, and organic acids dissolution. Dissolution during deep burial is insignificant. Pores are formed in near-surface and pre-oil window stages and effectively preserved till present. This result may be of great significance to the further exploration of deeply buried carbonate reservoirs not only in NE Sichuan Basin, but also around the world.展开更多
The Lower Triassic Feixianguan Formation at the well-known Puguang gasfield in the northeastern Sichuan Basin of southwest China produces a representa- tive oolitic reservoir, which has been the biggest marinesourced ...The Lower Triassic Feixianguan Formation at the well-known Puguang gasfield in the northeastern Sichuan Basin of southwest China produces a representa- tive oolitic reservoir, which has been the biggest marinesourced gasfield so far in China （discovered in 2003 with proven gas reserves greater than 350× 10^8 m3）. This study combines core, thin section, and scanning electron microscopy observations, and geochemical analysis （C, O, and Sr isotopes） in order to investigate the basic characteristics and formation mechanisms of the reservoir. Observations indicate that platform margin oolitic dolomites are the most important reservoir rocks. Porosity is dominated by intergranular and intragranular solution, and moldic pore. The dolomites are characterized by medium porosity and permeability, averaging at approximately 9% and 29.7 mD, respectively. ^87Sr/^86Sr （0.707536-0.707934） and δ^13CpDB （1.8 ‰--3.5 ‰） isotopic values indicate that the dolomitization fluid is predominantly concentrated seawater by evaporation, and the main mechanism for the oolitic dolomite formation is seepage reflux at an early stage of eodiagenesis. Both sedimentation and diagenesis （e.g., dolomitization and dissolution） have led to the formation of high-quality rocks to different degrees. Dolomite formation may have little contribution, karst may have had both positive and negative influences, and burial dissolution-TSR （thermochemical sulfate reduction） may not impact widely. The preservation of primary intergranular pores and dissolution by meteoric or mixed waters at the early stage of eogenesis are the main influences. This study may assist oil and gas explorationactivities in the Puguang area and in other areas withdolomitic reservoirs.展开更多
文摘The deeply buried shoal dolomite reservoirs of the Lower Triassic Feixianguan Formation, giant Puguang Gas Field, NE Sichuan Basin, are exceptionally porous. The influences of diageneses on pore evolution are studied. Through petrologic investigation, diagenetic phases are divided into four stages, i.e., near-surface, pre-oil window, oil window, and gas window. The Adobe Photoshop system is used to quantify the rock texture components, porosity constitutions and the influences of diageneses on reservoir porosity. Porosity evolution curves are quantitatively recovered. The Feixianguan reservoir porosities are mainly created by early meteoric dissolution, dolomitization, and organic acids dissolution. Dissolution during deep burial is insignificant. Pores are formed in near-surface and pre-oil window stages and effectively preserved till present. This result may be of great significance to the further exploration of deeply buried carbonate reservoirs not only in NE Sichuan Basin, but also around the world.
文摘The Lower Triassic Feixianguan Formation at the well-known Puguang gasfield in the northeastern Sichuan Basin of southwest China produces a representa- tive oolitic reservoir, which has been the biggest marinesourced gasfield so far in China （discovered in 2003 with proven gas reserves greater than 350× 10^8 m3）. This study combines core, thin section, and scanning electron microscopy observations, and geochemical analysis （C, O, and Sr isotopes） in order to investigate the basic characteristics and formation mechanisms of the reservoir. Observations indicate that platform margin oolitic dolomites are the most important reservoir rocks. Porosity is dominated by intergranular and intragranular solution, and moldic pore. The dolomites are characterized by medium porosity and permeability, averaging at approximately 9% and 29.7 mD, respectively. ^87Sr/^86Sr （0.707536-0.707934） and δ^13CpDB （1.8 ‰--3.5 ‰） isotopic values indicate that the dolomitization fluid is predominantly concentrated seawater by evaporation, and the main mechanism for the oolitic dolomite formation is seepage reflux at an early stage of eodiagenesis. Both sedimentation and diagenesis （e.g., dolomitization and dissolution） have led to the formation of high-quality rocks to different degrees. Dolomite formation may have little contribution, karst may have had both positive and negative influences, and burial dissolution-TSR （thermochemical sulfate reduction） may not impact widely. The preservation of primary intergranular pores and dissolution by meteoric or mixed waters at the early stage of eogenesis are the main influences. This study may assist oil and gas explorationactivities in the Puguang area and in other areas withdolomitic reservoirs.
