Jurassic Gas Research Articles

Differential enrichment mechanism of helium in the Jinqiu gas field of Sichuan Basin, China

Helium is extensively utilized in aerospace, healthcare, electronics, semiconductors, advanced science, and renewable energy sectors, playing a pivotal role in the advancement of human technology. Presently, helium is primarily extracted from natural gas as an associated resource. The cost of extraction decreases with an increase in the helium concentration within the gases. Therefore, understanding the mechanisms involved in helium generation, migration, and accumulation underground is vital. This article delves into the differential enrichment mechanism of helium in the Jinqiu gas field, situated in the Sichuan Basin of China, by analyzing the molecular and isotopic composition characteristics of the major gases and noble gases, employing gas dissolution and diffusion models. Compared with other Jurassic gas reservoirs in the Sichuan Basin, the Jinqiu gas field contains a significantly higher helium concentration, displaying unique enrichment patterns within its area. The majority of hydrocarbon gases originate from the local underlying Triassic Xujiahe Formation source rocks. Specifically, the western section of the Jinqiu field is primarily supplied by the higher maturity Xujiahe Formation source rocks located in the western Sichuan Basin. Notably, there is no significant contribution of mantle-derived volatile components in the Jinqiu field. Helium and argon are primarily radiogenic, whereas neon primarily originates from atmosphere. The good linear correlation between 4He and 20Ne suggests that their transfer is primarily facilitated through groundwater. The solubility calculation reveals that the helium exsolved from the in-situ pore water of the reservoir, due to stratigraphic uplift during the Himalayan movement, comprises only 0.04%–0.11% of the existing reserves. This suggests that gas desolvation plays a relatively minor role in helium enrichment in the Jinqiu field. Additionally, the calculation results of gas diffusion indicate that diffusion's contribution to helium enrichment in the Jinqiu gas field remains minimal. Finally, our analysis of methane reserve changes suggests that the combined effect of differential loss and dilution of hydrocarbon gases is the primary mechanism for helium's differential enrichment in the Jinqiu field. Notably, methane and carbon dioxide depletion may be a significant factor in helium enrichment within the crustal natural gas system.

Geological and Geochemical Characteristics of the Terrestrial Lower Jurassic Shale in Tarim Basin and its Favorable Exploration Areas

Large amounts of conventional gas resources that originated from terrestrial Lower Jurassic shale were discovered in the Tarim Basin, indicating promising exploration prospects for shale gas resources, whereas limited understandings were obtained on the geological and geochemical characteristics of the Lower Jurassic shale. In this study, based on cores of exploration wells and field outcrops, total organic carbon (TOC) pyrolysis, microscopic composition, organic elements, vitrinite reflectance, x-ray diffraction, and methane isothermal adsorption experiments were carried out on Lower Jurassic shale in the Tarim Basin. The results show that the TOC content of shale is relatively high, but the TOC content of shale in different regions is quite different. Among them, the Kuqa Depression is the highest (more than 3%), the Southwest Tarim Basin is second (more than 1%), and the East Tarim Basin is the lowest. The main types of kerogen in shale are mainly type III and type II2. The thermal evolution maturity of shale in different regions is quite different; the highest Ro of shale in the Southwest Tarim Basin is more than 2.0% and that of shale in the Kuqa depression is higher than 1.5%, both of which have entered the stage of high-over-mature evolution, and the shale in the East Tarim Basin is only in the low maturity–mature stage. The overall content of brittle minerals such as quartz in shale is greater than 40%, which has good fracturing properties. The adsorbed gas content of shale is high, but there is a great difference (0.5–4 m3/t), which is related to the large difference in the abundance of organic matter, thermal maturity, and clay mineral content of shale. Therefore, the Lower Jurassic shale gas in the Tarim Basin has good prospects for exploration. Based on the superposition method of the main controlling geological factors, it is predicted that the favorable areas for shale gas exploration are mainly located in the Keshen and Yinan-Yeyun areas of the Kuqa Depression and the Caohu Sag-Mandong area of the East Tarim Basin. This research not only provides basic data for the evaluation of shale gas resources in our country, but also provides certain guidance for the exploration of Lower Jurassic shale gas in the Tarim Basin.

Geochemical characteristics of natural gas in tight sandstone of the Chengdu large gas field, Western Sichuan Depression, Sichuan Basin, China

SINOPEC has made significant progress in natural gas exploration in terrigenous tight sandstone in the Western Sichuan Depression, making it one of the predominant exploration areas in the Sichuan Basin. Although the Chengdu large gas field was located in the main reservoirs of Upper Jurassic tight sandstone, few geochemical proofs were presented to support the explanation of the gas source, and regional differences in natural gas have been poorly investigated. The Jurassic tight gas in the Chengdu large gas field has a dryness coefficient (C1/C1-5) of 0.939–0.982, and the δ13C1, δ13C2, and δD1 values range from −33.7‰ to −30.7‰, −25.4‰ to −22.3‰, and −162‰ to −153‰, respectively, with positive carbon and hydrogen isotopic series of gaseous alkanes. The carbon and hydrogen isotopic compositions of the Jurassic tight gas indicate that it is typically coal-derived gas. The measured vitrinite reflectance (RO) values of source rocks of Member 5 of the Xujiahe Formation, which are demonstrated as the main source of Jurassic tight gas, are consistent with the calculated RO values according to the two-stage fractionation model of coal-derived gas. Effective source rocks are rare in the Lower Jurassic Baitianba Formation of the study area, which is considered to have only a minor contribution to the Jurassic gas reservoirs. The geochemical characteristics of Jurassic natural gas from various gas fields in the Western Sichuan Depression vary depending on the effect of different gas sources and accumulation processes.

O21 - Topic: AS02-Epidemiology: CONDITIONAL RELATIVE SURVIVAL IN MYELODYSPLASTIC SYNDROMES REVEALS A PERMANENT EXCESS MORTALITY RISK FOR LONG-TERM SURVIVORS: A POPULATION-BASED STUDY IN THE NETHERLANDS

SINOPEC has made significant progress in natural gas exploration in terrigenous tight sandstone in the Western Sichuan Depression, making it one of the predominant exploration areas in the Sichuan Basin. Although the Chengdu large gas field was located in the main reservoirs of Upper Jurassic tight sandstone, few geochemical proofs were presented to support the explanation of the gas source, and regional differences in natural gas have been poorly investigated. The Jurassic tight gas in the Chengdu large gas field has a dryness coefficient (C1/C1-5) of 0.939–0.982, and the δ13C1, δ13C2, and δD1 values range from −33.7‰ to −30.7‰, −25.4‰ to −22.3‰, and −162‰ to −153‰, respectively, with positive carbon and hydrogen isotopic series of gaseous alkanes. The carbon and hydrogen isotopic compositions of the Jurassic tight gas indicate that it is typically coal-derived gas. The measured vitrinite reflectance (RO) values of source rocks of Member 5 of the Xujiahe Formation, which are demonstrated as the main source of Jurassic tight gas, are consistent with the calculated RO values according to the two-stage fractionation model of coal-derived gas. Effective source rocks are rare in the Lower Jurassic Baitianba Formation of the study area, which is considered to have only a minor contribution to the Jurassic gas reservoirs. The geochemical characteristics of Jurassic natural gas from various gas fields in the Western Sichuan Depression vary depending on the effect of different gas sources and accumulation processes.

Resource potential of the Jurassic gas system, northern margin of the Qaidam Basin, northwestern China

The main source rocks, hydrocarbon generative subbasins, hydrocarbon generation periods, resource potential, and the relationship between the trap evolution history and hydrocarbon generation history are important problems associated with oil and gas exploration. In this study, we develop a three-dimensional geological model with respect to the Mesozoic and Cenozoic strata of the northern margin of the Qaidam Basin based on the most recent geological data. Using this model, the burial depth, temperature, maturity, and gas generation history of the source rock, the plane diagram of the source-rock current maturity, the gas generation intensity map, and the amount of gas generation during each geological period and within different subbasins can be obtained. Based on the obtained maps, we can state that the maturity of the source rock controls the distribution of natural gas (i.e., natural gas is located within and in the vicinity of mature and highly mature source rocks). We also observed the following: (1) the Lower Jurassic section is the main gas source rock; (2) the Yibei subbasin is the main hydrocarbon generative subbasin, followed by the Kunteyi, Pingdong, and Lenghu subbasins; (3) the main gas generation period is after the upper member of the lower Ganchaigou Formation deposition, with maximum gas generation occurring during the upper Ganchaigou Formation deposition and gradually decreasing thereafter—the majority of the structures in the inner basin are formed after lower Youshashan Formation deposition, demonstrating the tectonic activity coincided with periods of natural gas formation; and (4) the amount of natural gas resource becomes 1.23 trillion cubic meters. From these analyses, we can demonstrate that the late tectonic belts formed in the four gas-generating subbasins exhibit considerable promise for exploration.

Lithofacies classification using Bayes theorem method : Case study Western Desert, Egypt

This paper shows the availability of using the Bayesian classification method to predict class membership probabilities in one of the deep tight reservoirs in Western Desert, Egypt. The workflow of our project that using the Bayesian method used the deterministic petrophysical results of three training wells to train the data and extract the classifiers. The classified data were modeled using Gaussian distribution for each lithofacies. The used wells were acquired from a deep Jurassic gas reservoir in the Western Desert of Egypt. The fitting between actual and modeled data has been reached by minimizing the L2 norm. Besides, a cross-validation process was used for validating the resulted classifiers. Finally, the Bayesian classification method can predict the GWC with an accuracy of 4 m. To avoid probability interference caused by the compacted shale more data should be added to the initial model.

The Jurassic Oil and Gas Source Rocks of Hydrocarbon Deposits in the Eastern Part of the Fukang Depression (Junggar Oil and Gas Basin)

In recent years, significant success has been achieved in the search for and exploration of oil and gas reservoirs in the Jurassic deposits on the eastern side of the Fukang Depression, which is the least studied part of the Junggar oil and gas basin. In order to determine the hydrocarbon generation source, we have studied source rocks, oil and oil-bearing sandstones (24 samples from 13 wells), from the Badaowan, Sangonghe, Xishanyao, Toutunhe, and Qigu productive reservoirs of the Fukang Depression research area. Based on these studies, the organic matter composition of the Jurassic source rocks, the properties and molecular composition of oils, as well as the composition characteristics of biomarkers in them have been examined in detail. According to the research data and interpretation results, Badaowan mudstones were the source rocks of oil in the Gumudi zone and Fukang Depression, as well as that in the Baijiahai and Shaqi ledges.

Characteristics and exploration potential of Jurassic oil and gas reservoirs in Mahu sag of the Junggar Basin

Characteristics and exploration potential of Jurassic oil and gas reservoirs in Mahu sag of the Junggar Basin

PREDICTION OF PARAMETERS FOR COMMERCIAL OIL-AND-GAS CONTENT ZONES OF JURASSIC SEDIMENTS IN THE NORTH OF WESTERN SIBERIA

Discovered hydrocarbon deposits in a number of fields are the characteristic of the industrial productivity of Jurassic sediments in the north of Western Siberia. Most of the deposits are in the Middle Jurassic sediments, the signs of hydrocarbons have been obtained in the Lower Jurassic sediments, single deposits have been obtained in the Upper Jurassic sediments. This uneven distribution of deposits in the Jurassic oil and gas bearing facility is associated with the complexity of its structure. Therefore, there is a need to conduct a comprehensive analysis of the geological structure of Jurassic sediments, to identify geological parameters to predict commercial oiland-gas content zones in the investigated territory.Based on the results of the study of deep drilling data, seismic survey in the north of Western Siberia, schematic maps of the depth zones of Jurassic sediments have been constructed, the author of the article determines the parameters of industrial productivity zones. The most significant parameter is abnormally high formation pressure. Based on the conducted researches, the author notes the prospective commercial oil-and-gas content zones for Jurassic sediments within NadymPur watershed.

Thermal modelling of gas generation and retention in the Jurassic organic-rich intervals in the Darquain field, Abadan Plain, SW Iran

The petroleum system with Jurassic source rocks is an important part of the hydrocarbons discovered in the Middle East. Limited studies have been done on the Jurassic intervals in the 26,500 km2 Abadan Plain in south-west Iran, mainly due to the deep burial and a limited number of wells that reach the basal Jurassic successions. The goal of this study was to evaluate the Jurassic organic-rich intervals and shale gas play in the Darquain field using organic geochemistry, organic petrography, biomarker analysis, and basin modelling methods. This study showed that organic-rich zones present in the Jurassic intervals of Darquain field could be sources of conventional and unconventional gas reserves. The organic matter content of samples from the organic-rich zones corresponds to medium-to-high-sulphur kerogen Type II-S marine origin. The biomarker characteristics of organic-rich zones indicate carbonate source rocks that contain marine organic matter. The biomarker results also suggest a marine environment with reducing conditions for the source rocks. The constructed thermal model for four pseudo-wells indicates that, in the kitchen area of the Jurassic gas reserve, methane has been generated in the Sargelu and Neyriz source rocks from Early Cretaceous to recent times and the transformation ratio of organic matter is more than 97%. These organic-rich zones with high initial total organic carbon (TOC) are in the gas maturity stage [1.5–2.2% vitrinite reflectance in oil (Ro)] and could be good unconventional gas reserves and gas source rocks. The model also indicates that there is a huge quantity of retained gas within the Jurassic organic-rich intervals.

Tracing natural gas migration by integrating organic and inorganic geochemical data: A case study of the Jurassic gas fields in western Sichuan Basin, SW China

Abstract Based on the integrated geochemical and isotopic analysis of natural gases, formation waters, authigenic minerals, and fluid inclusions, a set of organic and inorganic geochemical tracing parameters, including methane/ethane ratio (C1/C2), N2 content, arene/alkane ratio, carbon isotope of methane (δ13C1), total dissolved solids (TDS) and chemistry of formation water, oxygen and carbon isotopic composition of authigenic calcite cement (δ18Ocalcite and δ13Ccalcite), and homogenization temperature (Th) and salinity of hydrocarbon-bearing brine inclusions, have been proposed to indicate the phase, direction, and pathway of natural gas migration and to discuss the migration processes and mechanisms of the Jurassic hydrocarbon in western Sichuan. This study results reveal that the Middle Jurassic gases in western Sichuan depression mainly migrated in water-dissolving phase and have the characteristics of increase of arene/alkane ratio and δ13C1 during migration and desolubilization, lower TDS of gas-associated waters, light δ18Ocalcite and δ13Ccalcite in gas-bearing sands, and high Th and low salinity of hydrocarbon-bearing brine inclusions, while the Upper Jurassic gases primarily migrated in free gas phase. Additionally, it is demonstrated that the migration directions and pathways of the Jurassic gases in western Sichuan can be investigated effectively by applying multiple organic and inorganic geochemical tracing parameters, in combination with the study results of geological setting and phase state evolution of water-dissolved gases during desolubilization and accumulation.

Volcanic rock characterisation using the concept of Extended Elastic Impedance: A case study from a Middle Jurassic gas reservoir in offshore Western Australia

Successful identification of volcanic rocks is critical in reservoirs where they have been previously intersected. This is because they impact on reserve estimates and influence fluid flow behaviour. Various studies using seismic inversion data were performed to try to characterise volcanic rocks in a sandstone reservoir in the Plover Formation. We noted that traditional techniques such as cross-plots between P-Impedance (Ip) and Vp/Vs was not very effective in this reservoir due to significant facies overlap at seismic resolution and inversion data quality. Therefore volcanic rock identification was attempted using advanced seismic attribute analysis. This involved testing and evaluating other elastic attributes, either individually or in combinations, to try and segregate volcanic rocks from other lithofacies. Two approaches were adopted to find out a suitable single attribute to identify the volcanic rock: (i) scaling of elastic logs with a non-elastic trend; (ii) generating a single attribute using Ip, Is and LMR cross-plots. Log and seismic scale analysis proved the suitability of both methods in volcanic rock identification. Subsequently, Extended Elastic Impedance (EEI) was applied to generate the EEI equivalent of those single attribute yielding positive results.

Helium signatures of gases from the Sichuan Basin, China

Natural gases from the Sichuan Basin, China were analyzed to investigate helium abundances and isotopic composition in order to assess crustal vs. mantle inputs into the Sinian to Jurassic gas reservoirs that occur at depths up to 4900m. In general, gases from the Sinian and pre-Sinian strata in south Sichuan have relatively high abundances of helium compared to those from the east, central and west Sichuan, implying an increase of crustal helium with time. All gas samples demonstrate very low helium isotopic ratios (3He/4He designated R) with an average of 0.016 Ra (n=78, where Ra is the isotope ratio found in the atmosphere), indicative of a crustal origin. This is further supported by the relatively stable upper mantle found in west China. In contrast, the thin and active lithosphere in the east part of China is favorable for the injection of mantle-derived volatiles into gas reservoirs. This explains why gases from the east part of China generally have R/Ra>1 while those in the west have R/Ra⩽0.1.

Handling Jurassic Field Sour Gas Creates Challenges Upstream and Downstream

This article, written by Editorial Manager Adam Wilson, contains highlights of paper SPE 154452, ’Challenges in Sour-Gas Handling for Kuwait Jurassic Sour Gas,’ by Bader Nasser Al Qaoud, SPE, Kuwait Oil Company, prepared for the 2012 SPE Middle East Unconventional Gas Conference and Exhibition, Abu Dhabi, 23-25 January. The paper has not been peer reviewed. Kuwait Oil Company started free gas production from its Jurassic sour-gas field in May 2008 with the commissioning of Early Production Facility (EPF) 50. The field produces sour gas and light crude from a deep high-pressure/high-temperature naturally fractured carbonate reservoir with low permeability and low porosity. The well fluid is characterized by high hydrogen sulfide (H2S) (5%) and carbon dioxide (CO2) (5%) content. Handling such highly corrosive well fluid creates a wide range of challenges, from upstream at the wellhead to downstream at the processing facility. Upstream Challenges Upstream challenges for the Jurassic gas field have been related mostly to subsurface corrosion of tubing, unplanned well downtime because of hydrate formation during winter, and failure of automated chokes for some wells. Subsurface Tubing Corrosion. A moderate to severe corrosion rate has been indicated by corrosion logs in the production tubing because of the high H2S and CO2 content of the well fluid. Plans exist for existing carbon-steel tubing for four wells to be replaced by corrosion-resistant alloy material, and regular corrosion logs are being run for other suspect wells. Hydrate Formation in Flowlines. Hydrate formation has been observed in flowlines during winter for 11 wells when flowline temperature drops to 65°F. This has resulted in unplanned production loss and substantial well downtime. The best mitigation option implemented was the injection of kinetic hydrate inhibitor (KHI) at the wellhead at the onset of winter for the identified wells, and a good degree of success has been achieved. However, KHI is not very effective in controlling hydrates at temperatures below 4°C, and this is a problem that needs to be addressed as a priority. Flowline insulation at the point of restriction and heat tracing also have been implemented for four wells, with a fair amount of success. Challenges With Automated Chokes. Automated chokes were first installed in the field in April 2011. The purpose of automation was to improve control of remotely located wells, enhance safety, and ensure better control of field production. Sixteen Jurassic wells are currently on automated chokes of three different makes—M1, M2, and M3. Challenges With Make M1. The factory-set choke opening did not match actual choke opening. Choke adjustments had to be made with flowing wellhead pressure (FWHP) as a reference, and this leads to inaccurate settings. Scale formation also has been observed in-side the choke body, causing restricted flow and inaccurate FWHP readings and, therefore, poor monitoring of well performance.

Evaluation of Upper Triassic T3x5 Source Rocks (Western Sichuan Depression, Sichuan Basin) and their Hydrocarbon Generation and Expulsion Characteristics: Implication for Tight-Sand Gas and Shale Gas Accumulation Potential Assessment

An unconventional, continuous petroleum system consists of an accumulation of hydrocarbons that is found in low-matrix-permeability rocks and contain large amounts of hydrocarbons. Tight-sand gas in the Jurassic and shale gas within the fifth member of Xujiahe Formation (T3x5) are currently regarded as the most prolific emerging unconventional gas plays in China. The conventional and systematical evaluation of T3x5 source rocks was carried out for the first time in the western Sichuan basin (WSD). Hydrocarbon generation and expulsion characteristics (including intensity, efficiency, and amount) of T3x5 source rocks were investigated. Results show that T3x5 source rocks are thick (generally >200 m), have high total organic content (TOC, ranging from 2.5 to 4.5 wt%), and dominated by III-type kerogen. These favorable characteristics result in a great hydrocarbon generating potential under the high thermal evolution history (Ro > 1.2%) of the area. An improved hydrocarbon generation potential methodology was applied to well data from the area to unravel the hydrocarbon generation and expulsion characteristics of T3x5 source rocks in the WSD. Results indicate that the source rocks reached hydrocarbon expulsion threshold at 1.06% Ro and the comprehensive hydrocarbon expulsion efficiency was about 60%. The amount of generation and expulsion from T3x5 source rocks was 3.14 × 1010 and 1.86 × 1010 t, respectively, with a residual amount of 1.28 × 1010 t within the source rocks. Continuous-type tight-sand gas was predicted to develop in the Jurassic in the Chengdu Sag of the WSD because of the good source-reservoir configuration (i.e., the hydrocarbon generation and expulsion center was located in Chengdu Sag), the Jurassic sandstone reservoirs were tight, and the gas expelled from the T3x5 source rocks migrated for very short distances vertically and horizontally. The amount of gas accumulation in the Jurassic reservoirs derived from T3x5 source rocks is up to 9.3 × 108 t. The T3x5 gas shale has good accumulation potential compared with several active US shale-gas plays. Volumetrically, the geological resource of shale gas is up to 1.05 × 1010 t. Small differences between the amounts calculated by volumetric method compared with that by hydrocarbon generation potential methodology may be due to other gas accumulations present within interbedded sands associated with the gas shales.

Ongoing Development of Cementing Practices and Technologies for Kuwait Oil Company's Deep HP/HT Exploration and Gas Wells: Case History

Summary Exploration activities in Kuwait have been focused on the search for high-quality oil from the Jurassic formations and gas in the Triassic/Permian series. The wells drilled to these prospects are very challenging because of high-pressure/high-temperature (HP/ HT) conditions, large casing sizes, oil-based mud, the presence of high levels of H2S and CO2, and a narrow pore-/fracture-pressure window. In particular, the cementing of the deep strings in these wells has been extremely challenging. Over the last 8 years, a concentrated effort has been made to introduce new technologies and materials to improve the cementing practices both from operational and safety aspects. In 2003, the success ratio for deep cementations was highly variable. The Kuwait Oil Company (KOC), along with one of their cementing service providers, worked on a series of changes to practices and materials with the aim of improving job quality with high repeatability. This was based primarily on the technologies being developed in HP/HT wells around the globe, especially in the North Sea, and it resulted in a notable improvement in cementing performance. Technologies and practices that had been developed include spacer technology, application of synthetic retarders, fluid-loss and antigas-migration additive improvements, development of finegrained weighting additives, use of HP/HT rheometers, systematic product control, the minimizing of handling, and safer mixing practices at the wellsite. This paper will discuss the application of these technologies, materials, and practices over an 8-year period as a case history to illustrate the improvements made in achieving consistent cement quality and final slurry placement for the deep-casing and liner strings, and will conclude with recommendations and lessons learned during this process.

Carbon Isotopic Characteristics of Jurassic Alkane Gases in the Sichuan Basin, China

There are plentiful natural gas resources in Jurassic in the Sichuan basin, where a lot of gas fields (reservoirs) have been discovered, and the natural gas is mainly alkane gas. Comprehensive study on carbon isotopic characteristics indicated that Jurassic alkane gas in Sichuan Basin can be divided into two types, coal-formed gas and oil-type gas. As the majority of the natural gas, coal-formed gas distributed in Central and Northwest gas districts and was mainly from the underlying coal-measure hydrocarbon source rocks in Xujiahe Formation. The carbon isotopic series were mainly normal, while a minority were reversed. The reversal ones in Northwest gas district were caused by mixing of gases from the same source rocks with different maturity, while those in Central gas district were caused by mixing of oil-type and coal-formed gases. Oil-type gas was only discovered in Bajiaochang gas field in Central oil and gas district, and derived from self-generation and self-accumulation in Lower Jurassic, with normal carbon isotopic series and without any reversal. Comprehensive analysis suggested that the carbon isotopic characteristics of Jurassic alkane gas were different according to different regions and layers. The δ13C1 and δ13C2 values of Jurassic alkane gas in central area were significantly lower than those in northwestern area for the influence by oil-type gas generated from Lower Jurassic Ziliujing Formation.

Characteristics of Triassic Petroleum Systems in the Longmenshan Foreland Basin, Sichuan Province, China

Abstract: The Triassic in the Longmengshan foreland basin is rich in oil and gas resources. Its reservoirs feature low‐porosity, low‐permeability, small pore throat, high water saturation, and strong heterogeneity. The existence of abnormally high pressure and various reservoir‐cap combinations developed at different times provide favorable conditions for trapping oil and gas. Taking the theory of petroleum systems as a guide, and beginning with research on tectonics, sedimentary history, distribution and evolution of source rocks, reservoir evolution, hydraulic force distribution, and hydrocarbon migration, analysis and study of static factors like source rocks, reservoirs and cap rocks, and dynamic factors such as hydrocarbon generation, migration, and accumulation revealed the characteristics of the Upper Triassic petroleum system in western Sichuan province. The deep‐basin gas in the central hydrocarbon kitchen of the Upper Triassic, structural‐lithological combination traps on the surrounding slopes, and the structural traps of the Indo‐Chinese‐Yangshan paleohighs, are potential plays. The relatively well‐ developed fault zones in the southern segment of the Longmengshan foothill belt are favorable Jurassic gas plays. Pengshan‐Xinjin, Qiongxi, and Dayi are recent exploration targets for Jurassic oil/gas reservoirs.

Accumulation characteristics and the main controlling factors of Lunnan multilayer oil province, Tarim Basin, China

Lunnan region is a large-scale paleohigh with many coexisting oil and gas bearing series. At present, about 2 billions tons of proved, probable and possible oil and gas reverses have been proved there. Eight oil and gas bearing series have been found in the Ordovician, Carboniferous, Triassic and Jurassic of Lunnan region, they all bear the characteristics of large-scale multilayer oil-gas province. Ordovician is the main reservoir series where over 0.8 billion tons of oil geologic reserves were discovered, and a super large-scale marine carbonate oil and gas field has formed. Reservoir space of the carbonate reservoirs is mainly composed of dissolved hole, dissolved pore and fracture in Lunnan paleo-burial hill. Generally, dissolved holes are widely distributed among them. Reservoir developments are mainly controlled by karstification and tectonic disruption. Due to the similar geochemical characters, the Ordovician, Carboniferous, Triassic and Jurassic oil and gas reservoirs present the same oil source rock of Mid-Upper Ordovician, the latter except Ordovician are mostly of secondary oil and gas reservoirs migrated vertically by faults during the process of multiple phase tectonic movement, adjustment and reconstruction. Lunnan composite oil and gas accumulation region is situated in the vicinity of large-scale hydrocarbon generation depressions in three directions, ample oil and gas from hydrocarbon generation depressions supplied the adjacent oil and gas reservoirs once. Hereby, the succeed paleohigh is the long-term hydrocarbon accumulation region, which is favor for the formations of high quality reservors, fault systems and huge-scale composite oil and gas accumulation.

Kinetics of hydrocarbon generation for Well Yingnan 2 gas reservoir, Tarim Basin, China

Well Yingnan 2, an important exploratory well in the east of Tarim Basin, yields high commercial oil and gas flow in Jurassic. Natural gas components and carbon isotopic composition indicate that it belongs to sapropel type gas. Because this region presents many suits of hydrocarbon source rocks, there are some controversies that natural gases were generated from kerogen gas or crude oil cracking gas at present. By using the kinetics of hydrocarbon generation and carbon isotope, natural gas of Well Yingnan 2 is composed mainly of crude oil cracking gas, about 72%, it is generated from secondary kerogen gas of Cambrian-Lower Ordovician source rock and crude oil cracking gas of Mid-Upper Ordovician oil reservoir. The main oil and gas filling time is 65 Ma later in the Jurassic gas reservoir of Well Yingnan 2, so the gas reservoir belongs to late accumulation and continuous filling type.