Insights from fluid inclusions, thermal and PVT modeling for paleo-burial and thermal reconstruction of the Córdoba petroleum system (NE Mexico)

Carbonate reservoirs in the Córdoba petroleum system (NE Mexico) passed through a multiphase deformation history complicating the petroleum geology. The area evolved from passive margin and foreland setting to Laramide fold and thrust belt (FTB) that was subsequently buried below the Tertiary-Quaternary Veracruz Basin, which in turn underwent transpressional deformation. Reconstruction of paleo-burial (erosion) and paleo-thermicity through the different zones of the FTB and adjacent foreland is a challenging task since classical calibration tools fail to discriminate between several kinematic and thermal models. In this study results from detailed diagenetic and fluid inclusion (FI) analyses on carbonates from the western part of the Córdoba Platform helped constraining paleo-thermicity. Combined microthermometry, synchrotron FTIR analyses and PVT modeling of cogenetic hydrocarbon-aqueous FI allowed also calculation of absolute pressures. Thermal modeling exercises calibrated with organic maturity parameters, bottom-hole temperatures or temperatures from FI demonstrate that without controlling also paleo-erosion the model results may be misleading.     

基于电缆地层测试的储层产能预测方法研究

通过对电缆地层压力测试资料和采集流体样品的PVT组分分析,提出了电缆地层测试储层产能预测的方法,为部分替代DST测试提供了理论基础。首先,利用曲线拟合方法精确求取地层有效渗透率和表皮系数等产能参数;利用采集流体样品的PVT组分分析,确定原油黏度、体积系数和溶解气油比等流体参数,结合电缆地层测试的产能方程,从而计算出储层的采油指数（PI）或单层日产量。     

The high-pressure and temperature equation of state of a majorite solid solution in the system of Mg4Si4O12-Mg3Al2Si3O12

The high-pressure and temperature equation of state of majorite solid solution, Mj_0.8Py_0.2, was determined up to 23 GPa and 773 K with energy-dispersive synchrotron X-ray diffraction at high pressure and high temperature using the single- and double-stage configurations of the multianvil apparatuses, MAX80 and 90. The X-ray diffraction data of the majorite sample were analyzed using the WPPD (whole-powder-pattern decomposition) method to obtain the lattice parameters. A least-squares fitting using the third-order Birch-Murnaghan equation of state yields the isothermal bulk modulus, K _T0  = 156 GPa, its pressure derivative, K′ = 4.4(±0.3), and temperature derivative (∂K _T /∂T) _P = −1.9(±0.3)× 10⁻² GPa/K, assuming that the thermal expansion coefficient is similar to that of pyrope-almandine solid solution. Received: 5 October 1998 / Revised, accepted: 24 June 1999     

Reserve and Pressure Change of Paleo-oil Reservoir in Puguang Area,Sichuan Basin

The Puguang (普光) gas field is the largest gas field found in marine carbonates in China.The Feixiangnan (飞仙关) and Changxing (长兴) reservoirs are two such reservoirs that had been buried to a depth of about 7 000 m and experienced maximum temperature of up to 220 ℃ before uplift to the present-day depth of 5 000-5 500 m,with present-day thermal maturity between 2.0% and 3.0% equivalent vitrinite reflectance (Ro).Bitumen staining is ubiquitous throughout the Feixianguan and Changxing formations,with the greatest concentrations in zones with the highest porosity and permeability,suggesting that the solid bitumen is the result of in-situ cracking of oil.According to the distribution of bitumen in the core,the paleo-oil boundary can be approximately determined.The paleo-oil resource is calculated to be about (0.61-0.92)×109 t (average 0.76×109 t),and the cracked gas volume is about (380.80-595.80)×109 m3 (average 488.30×109 m3); at least 58.74% of cracked gas is preserved in Puguang gas field.The study area experienced not only the cracking of oil but also thermochemical sulfate reduction,resulting in large quantities of nonhydrocarbon gas,with about 15.2% H2S and 8.3% CO2,together with the structural reconfiguration.During the whole process,the great change of volume and pressure compels the PVTsim modeling software to simulate various factors,such as the cracking of oil,the thermochemical sulfate reduction (TSR) and the tectonic uplift in both isolated and open geological conditions,respectively.The results show that although any one of these factors may induce greater pressure changes in an isolated system than in a closed system,the oil cracking and C3+involving TSR lead to overpressure during the early stage of gas reservoir.Therefore,the tectonic uplift and the methane-dominated TSR,as well as the semi-open system contribute to the reducing pressure resulting in the current normal formation pressure.     

Petroleum accumulation in the deeply buried reservoirs in the northern Dongying Depression,Bohai Bay Basin,China: New insights from fluid inclusions,natural gas geochemistry,and 1-D basin modeling

The deeply buried reservoirs (DBRs) from the Lijin, Shengtuo and Minfeng areas in the northern Dongying Depression of the Bohai Bay Basin, China exhibit various petroleum types (black oil-gas condensates) and pressure systems (normal pressure-overpressure) with high reservoir temperatures (154–185 °C). The pressure-volume-temperature-composition (PVTX) evolution of petroleum and the processes of petroleum accumulation were reconstructed using integrated data from fluid inclusions, stable carbon isotope data of natural gas and one-dimensional basin modeling to trace the petroleum accumulation histories.The results suggest that (1) the gas condensates in the Lijin area originated from the thermal cracking of highly mature kerogen in deeper formations. Two episodes of gas condensate charging, which were evidenced by the trapping of non-fluorescent gas condensate inclusions, occurred between 29-25.5 Ma and 8.6–5.0 Ma with strong overpressure (pressure coefficient, P_c = 1.68–1.70), resulting in the greatest contribution to the present-day gas condensate accumulation; (2) the early yellow fluorescent oil charge was responsible for the present-day black oil accumulation in well T764, while the late blue-white oil charge together with the latest kerogen cracked gas injection resulted in the present-day volatile oil accumulation in well T765; and (3) the various fluorescent colors (yellow, blue-white and blue) and the degree of bubble filling (F_v) (2.3–72.5%) of the oil inclusions in the Minfeng area show a wide range of thermal maturity (API gravity ranges from 30 to 50°), representing the charging of black oil to gas condensates. The presence of abundant blue-white fluorescent oil inclusions with high Grain-obtaining Oil Inclusion (GOI) values (35.8%, usually >5% in oil reservoirs) indicate that a paleo-oil accumulation with an approximate API gravity of 39–40° could have occurred before 25 Ma, and gas from oil cracking in deeper formations was injected into the paleo-oil reservoir from 2.8 Ma to 0 Ma, resulting in the present-day gas condensate oil accumulation. This oil and gas accumulation model results in three oil and gas distribution zones: 1) normal oil reservoirs at relatively shallow depth; 2) gas condensate reservoirs that originated from the mixture of oil cracking gas with a paleo-oil reservoir at intermediate depth; and 3) oil-cracked gas reservoirs at deeper depth.The retardation of organic matter maturation and oil cracking by high overpressure could have played an important role in the distribution of different origins of gas condensate accumulations in the Lijin and Minfeng areas. The application of oil and gas accumulation models in this study is not limited to the Dongying Depression and can be applied to other overpressured rift basins.     

位涡趋势诊断方法在高分辨率模式资料中的应用

位涡趋势（Potential Vorticity Tendency,PVT）诊断方法已经在台风移动研究中得到较多的应用,但是多用于水平分辨率几千米的模式输出资料。发现用位涡趋势方法诊断台风移动时,模式资料输出时间间隔必须与模式空间分辨率匹配,这是因为位涡趋势方法需要同时用时间和空间差分方法计算位涡的趋势和分布。当模式水平分辨率高于1 km时,模式可以模拟小尺度系统,相应的模式输出时间间隔必须缩短,使得模式输出资料能够代表小尺度系统的变化趋势。由于小尺度系统导致的位涡变化不能直接影响台风移动,建议应用两种方法解决位涡趋势方法中的时、空匹配问题:（1）当空间分辨率增加时,相应缩短模式输出资料的间隔;（2）不改变模式输出时间间隔,对计算位涡的物理量进行空间平滑,滤去小尺度系统的影响。