Origin of gas condensate reservoir in Fuman Oilfield, Tarim Basin, NW China

To understand the reservoir property and hydrocarbon accumulation conditions of the Middle and Upper Ordovician intraplatform shoal between ultra-deep main strike-slip faults in Fuman Oilfield of the Tarim Basin, China, the main strike-slip faults in and around well FD1 in the basin were analyzed in terms of sedimentary facies, sequence stratigraphy, intraplatform shoal reservoir property, and oil and gas origins, based on drilling data. The Yingshan Formation intraplatform shoal between the main strike-slip faults is superimposed with low-order faults to form a new type of hydrocarbon play. Firstly, hydrocarbons generated from the Lower Cambrian Yuertusi Formation source rocks vertically migrated into the second member of Yingshan Formation through the main strike-slip faults, and then migrated laterally until they were accumulated. A small amount of oil from Well FD1 came from the Yuertusi Formation source rocks in the mature stage, and a large amount of gas originated from oil cracking in the ultra-deep reservoirs. Therefore, the secondary gas condensate reservoir in Well FD1 is characterized by high gas to oil ratio, dry gas (dryness coefficient being 0.970) and hybrid origin. This new type of hydrocarbon play characterized by intraplatform shoal and low-order fault suggests a prospect of continuous hydrocarbon-bearing area in Fuman Oilfield, which will expand the ultrap-deep oil and gas exploration in the oilfield.

Cocracking and Separate Cracking of Straight-Run Gasoline and Light Gas Oil

This paper presents experimental results of cocracking of straight-run gasoline (SRG) and light gaS oil (LGO) in an improved pulsed-micro-pyrolyzer. It is shown that there are negative opergistic effect on the yields and selectivities of ethylene and propylene in cocracking. The difference in coking tendencies betWeen the cocracking and the separate cracking is compared as well.

Stable carbon isotopes of gaseous alkanes as genetic indicators inferred from laboratory pyrolysis experiments of various marine hydrocarbon source materials from southern China

Using high pressure and geological condition simulation vessels, we conducted hydrous pyrolysis experiments of kerogen, solid bitumen and liquid hydrocarbons in southern China in order to study the processes of gas generation and derive geo- chemical indicators of gas genesis under approximate pressure and temperature. The results indicate that gas generation productivity of different marine material decreased in the ganic matter （solid bitumen and heavy oil）, and kerogen. order of crude oil （light oil and condensate）, dispersed soluble or- Under identical temperature-pressure regimes, pyrolysates derived from kerogen and dispersed soluble organic matter display drastically different geochemical characteristics. For example, the δ13Cc02-δ13C1 values of gaseous products from dispersed soluble organic matter are greater than 20%o, whereas those from kerogen are less than 20%~. The 813C1 values of pyrolysates from different marine hydrocarbon sources generally increase with pyrolysis temperature, but are always lower than those of the source precursors. The δ13C values of ethane and propane in the pyrolysates also increase with increasing pyrolysis temperature, eventually approaching that of their sources, at peak hydro- carbon generation. At high-over mature stages, the δ13C values of ethane and propane are often greater than those of their sources but close to those of coal gases, and thus become ineffective as gas genetic indicators. Ln（CffC3） can clearly distin- guish kerogen degradation gas from oil cracking gas and Ln（CJC2）-（δ13C1-δ13C2） can be an effective indicator for distinguishing oil cracking gas from dispersed soluble organic matter cracking gas.

Characteristics and accumulation mode of large-scale Sinian-Cambrian gas reservoirs in the Gaoshiti-Moxi region, Sichuan Basin

The Sinian-Cambrian formations of the Sichuan Basin have favorable hydrocarbon accumulation conditions,but the exploration for large-scale gas fields is quite challenging due to old strata and multiple tectonic movements.Since the Weiyuan Sinian large gas field was found in 1964,the largest monoblock gas field(Anyue Gasfield)was discovered in the Cambrian Longwangmiao Formation of the Moxi region in 2013 with proven gas reserves of 440.1×109 m3.Total proven,probable and possible reserves exceed one trillion cubic meters in the Sinian Dengying Formation and the Cambrian Longwangmiao Formation of the Gaoshiti-Moxi region.The natural gas components,light hydrocarbons,reservoir bitumen abundance and other evidences prove that the dry natural gas was mainly derived from oil-cracking,with methane(a content of 82.65%-97.35%),ethane(a content of 0.01%-0.29%),nitrogen(a content of 0.44%-6.13%),helium(a content of 0.01%-0.06%),and hydrogen sulphide(0.62-61.11 g/m^(3)).Gas reservoir pressure increases gradually from the Sinian normal pressure(a pressure coefficient of 1.07-1.13)to high pressure(a pressure coefficient of 1.53-1.70)in the Cambrian Longwangmiao Formation.The temperature of the gas reservoir is 137.5-163 ℃.Gas reservoir traps are divided into three categories:tectonic type,tectonic-formation type and tectonic-lithologic type.The large-scale enrichment of the Sinian-Cambrian natural gas results from effective configuration of the large stable inherited palaeo-uplift during the Tongwan tectonic movement,wide distribution of ancient source rocks,high-quality reservoirs with vast pore-cavity,crude oil cracking of large palaeo-reservoirs and favorable preservation conditions.According to the palaeo-structure pattern prior to crude oil cracking of the palaeo-reservoirs,and bitumen abundance as well as the distribution characteristics of current gas reservoirs,the accumulation patterns of the cracking gas reservoir can be classified into three types:accumulation type,semi-accumulation and semi-dispersion type,and dispersion type.This understanding will play an important role in guiding the exploration of the Sinian-Cambrian natural gas exploration in the Sichuan Basin.