2nd Members Research Articles

Gas source of the Middle Jurassic Shaximiao Formation in the Zhongjiang large gas field of Western Sichuan Depression: Constraints from geochemical characteristics of light hydrocarbons

The Zhongjiang gas field is a typical large gas field in terrigenous strata of the Western Sichuan Depression. It remains debatable which member of the Upper Triassic Xujiahe Formation served as the source rocks and how significant the member contributed to the gas accumulations in the Zhongjiang gas field. In this study, we analyzed the essential characteristics of the Lower Jurassic source rocks and the geochemical features of light hydrocarbons in natural gas from the 2nd (T3x2) and 4th members (T3x4) of the Upper Triassic Xujiahe Formation (T3x), as well as the Middle Jurassic Shaximiao (J2s) and Qianfoya (J2q) formations. Based on this, we explored the sources of the natural gas in the Zhongjiang gas field and determined the natural gas migration patterns and their effects on the properties of light hydrocarbons in the natural gas. The results indicate that the Lower Jurassic lacustrine source rocks of the Zhongjiang gas field contain humic organic matter, with vitrinite reflectance (Ro) values ranging from 0.86% to 0.98%. Samples meeting the criterion for effective source rocks [total organic carbon (TOC) content ≥0.75%] exhibited an average TOC content of merely 1.02%, suggesting significantly lower hydrocarbon generation potential than source rocks in the underlying T3x, which show higher thermal maturity and TOC contents. For natural gas samples from T3x2, T3x4, J2s, and J2q reservoirs, their C5–7 iso-alkane content was significantly higher than their n-alkane content, and their methylcyclohexane (MCH) index ranged from 59.0% to 77.3%, indicating the predominance of methylcyclohexane in C7 light hydrocarbons. As indicated by the origin identification and gas-source correlation based on the geochemical features of light hydrocarbons, the natural gas in the Zhongjiang gas field is typical coal-derived gas. The gas from the primary pay zone of the Shaximiao Formation, with significantly high K1, (P2 + N2)/C7, and P3/C7 values, predominantly originated from the 5th member of the T3x and migrated in the free phase, with a small amount possibly sourced from the Lower Jurassic source rocks. The dissolution and adsorption during gas migration led to a decrease in the aromatic content in C6–7 light hydrocarbons and an increase in the iso-heptane values. Therefore, their effects must be considered when determining the gas origin and thermal maturity based on the aromatic content in C6–7 light hydrocarbons and iso-heptane values.

Structural attributes, evolution and petroleum geological significances of the Tongnan negative structure in the central Sichuan Basin, SW China

The Tongnan secondary negative structure in central Sichuan Basin has controls and influences on the structural framework and petroleum geological conditions in the Gaoshiti-Moxi area. To clarify the controls and influences, the deformation characteristics, structural attributes and evolution process of the Tongnan negative structure were investigated through a series of qualitative and quantitative methods such as balanced profile restoration, area-depth-strain (ADS) analysis, and structural geometric forward numerical simulation, after comprehensive structural interpretation of high-precision 3D seismic data. The results are obtained in three aspects. First, above and below the P/AnP (Permian/pre-Permian) unconformity, the Tongnan negative structure demonstrates vertical differential structural deformation. It experiences two stages of structural stacking and reworking: extensional depression (from the Sinian Dengying Formation to the Permian), and compressional syncline deformation (after the Jurassic). The multi-phase trishear deformation of the preexisting deep normal faults dominated the extensional depression. The primary depression episodes occurred in the periods from the end of Late Proterozoic to the deposition of the 1st–2nd members of the Dengying Formation, and from the deposition of Lower Cambrian Longwangmiao Formation–Middle–Upper Cambrian until the Ordovician. Second, the multi-stage evolution process of the Tongnan negative structure controlled the oil and gas migration and adjustment and present-day differential gas and water distribution between the Tongnan negative structure and the Gaoshiti and Moxi-Longnüsi structural highs. Third, the Ordovician, which is limitedly distributed in the Tongnan negative structure and is truncated by the P/AnP unconformity on the top, has basic geological conditions for the formation of weathering karst carbonate reservoirs. It is a new petroleum target deserving attention.

The delta-fluvial evolution of a lacustrine basin with gentle slope and low sedimentation rate: A case study of the Fudong Slope, Junggar Basin, Northwest China

Gentle slope belts of lacustrine basins are important areas for the generation of stratigraphic petroleum reservoirs controlled by sedimentary systems. Based on coring, well logging, 3D seismic and analytical test data, the sedimentary system and sandbody distribution characteristics of the Jurassic Toutunhe Formation (J2t) in the Fudong slope of the Junggar Basin were analysed. The results indicated that the Fudong slope showed the characteristics of low sediment input. Sediments mainly originated from the Shaqi uplift, and the sediment input gradually weakened from the early to the late J2t stages. The sedimentary system evolved from a delta to a meandering river, resulting in a delta front facies in the 1st member (J2t1) and a meandering river facies in the 2nd (J2t2) and 3rd (J2t3) members of the Toutunhe Formation. A sedimentary evolution pattern for the gentle slope with low sediment input was established. Thick deltaic sandbodies developed locally in the J2t1 stage. However, meandering rivers with high sinuosities predominantly developed and resulted in a striped geometry in the J2t2 and J2t3 members. Moreover, the meandering sandbodies exhibited an anastomosing morphology after multistage superposition. The channel and point bar facies in J2t2 were more developed than those in J2t3 because of sediment input differences. Under low-sediment input conditions, the sedimentary environment of the gentle slope belt in the lacustrine basin was controlled by changes in the palaeoclimate, palaeogeomorphology, gradient (slope) and base level. Palaeoclimate was the main factor controlling the evolution of the sedimentary environment. Palaeogeomorphology and slope controlled the distribution of sedimentary microfacies, channel sinuosity and sandbodies. Base-level change restricted the sandbody superimposition style. Under the low sediment input conditions of the Fudong slope, the subaqueous distributary channels of the delta environment and the point bars of the meandering river environment in the transitional belt of the Fudong slope are the main potential targets for stratigraphic petroleum reservoirs, whilst the 2nd member of the Toutunhe Formation (J2t2) is the main favourable interval for stratigraphic reservoir exploration.

Channel Evolution under the Control of Base-Level Cycle Change and the Influence on the Sustainable Development of the Remaining Oil—A Case in Jiang Ling Depression, Jiang Han Basin, China

The extension of river channels is one of the key factors in determining the remaining oil distribution. Different sedimentary facies and bedding types of oil layers will form specific characteristics of remaining oil distribution after water injection development. Using massive drilling, core, logging, seismic, and production data, on the basis of sequence stratigraphy base-level cycle change, the river records and development history are restored, and the fine connectivity of reservoirs and the configuration relationship of production wells are studied. The following conclusions are drawn: (1) A sequence stratigraphic division scheme is established. In the established sequence framework, the types and characteristics of reservoir sand bodies are analyzed. The 2nd and 6th members of Yu yang formation can be divided into 2 long-term base level cycles, 5 medium-term base level cycles, and 17 short-term base level cycles. The evolution of the second and sixth members of the Yu yang formation shows a pattern of base level rising, falling and rising again; (2) the vertical sedimentary evolution sequence is underwater distributary channel distributary channel meandering channel distributary channel flood plain. The types of channel sand bodies developed from little overlap to more vertical or lateral overlap and then gradually changed to isolated type; (3) according to the structural location and development sequence, different types of reservoirs are identified. Combined with the statistics of the drilled data of Yu yang formation k2y4 in Fu I fault block, it is found that the connectivity rate of oil layer thickness (the ratio of oil layer connectivity thickness to total thickness of sand layer) within the oil-bearing area is 84.4%, and the connectivity rate of the number of layers (8) is 60%. The connectivity condition is relatively good.

Calculating the formation period of fault lateral sealing and its application

The study aims to find out the formation period of fault traps near faults in petroliferous basins, based on an analysis of the formation period of fault lateral sealing and related influential factors. A method to calculate the formation period of fault lateral sealing (i.e. the time when displacement pressure of fault rock is equal to that of reservoir rock in fault wall with hydrocarbon migration) is established by comparing the relationship between displacement pressure and time for fault rock and reservoir rock. This method is then applied to the study on reservoirs in the 1st, 2nd, and 3rd members of Dongying Formation (E3d1, E3d2 and E3d3) in terms of formation period of lateral sealing of F3 fault crossing the three reservoirs in the No.5 structure of Nanpu Sag in Bohai Bay Basin. The results indicate that the formation period of the lateral sealing in the studied reservoirs can date from 7.1 Ma, 7.4 Ma and 9.2 Ma respectively, all prior to the hydrocarbon accumulation period (about 2.58 Ma). Hence, it can be concluded that these reservoirs are favorable for the accumulation and preservation of hydrocarbons generated from the underlying source rock E3s3, and the method proposed is feasible in calculating the formation period of fault lateral sealing.

Genetic types of natural gas and gas-source correlation in different strata of the Yuanba gas field, Sichuan Basin, SW China

The chemical compositions and stable carbon and hydrogen isotopic compositions of natural gases in different strata of the Yuanba gas field in the Sichuan Basin were analyzed to investigate their genetic types and source. Natural gases from the Permian Changxing and Triassic Feixianguan formations have dryness coefficients higher than 0.995 and contain H2S in most gas samples, having a positive correlation between the H2S and CO2 contents. The identification of gas origin and gas-source correlation from this study indicate that natural gas in the Ziliujing Formation and most gas samples from the Xujiahe Formation are coal-type gas produced from primary cracking of kerogen, and they are self-sourced reservoirs in relatively independent systems. The natural gases in the 1st and 2nd members of the Xujiahe Formation were mixed with minor amounts of oil-type gas from argillaceous carbonate rocks in the Leikoupo Formation. In addition to the self-accumulated oil-type gas in the Leikoupo Formation, natural gas mainly came from the overlying or lateral source rocks in the Xujiahe Formation. The H2S-bearing natural gases in the Changxing and Feixianguan formations were produced by the cracking of crude oil from source rocks in the underlying Wujiaping Formation, with partial contributions from certain local source rocks in the Permian Dalong Formation. The H2S-bearing natural gas has undergone the thermochemical sulfate reduction (TSR) which were dominated by heavy hydrocarbons. The high δ13C values of CO2 in these gas reservoirs mainly result from the interaction between acidic fluids and carbonate rocks in the reservoirs.

Familial multiple sclerosis patients have a shorter delay in diagnosis than sporadic cases

BackgroundThe diagnosis of multiple sclerosis (MS) is still complicated despite improvement in diagnostic guidelines. This means that time from first symptom to diagnosis in some cases is prolonged. Many aspects of MS aetiology are unknown, but the involvement of a genetic component is well established. This is also highlighted by the occurrence of familial MS cases, which represent 10–20% of all MS cases. We hypothesize that subsequent family members in a MS family, have a shorter time from onset of disease to diagnosis compared to sporadic MS cases. To investigate this, we have conducted a register study comparing time from onset to diagnosis in familial and sporadic MS cases. MethodsThis is a nationwide register study based on information from the Danish Multiple Sclerosis Registry and the Danish Civil Registration System. We included familial (first-degree relatives) and sporadic MS cases and calculated time lag between onset and diagnosis of MS for sporadic MS cases and for1st, 2nd and 3rd family members within the MS families. Median test and Cox regression were the statistical methods used to compare the familial and sporadic groups. ResultsWe found that 2nd and 3rd affected family member had a significant shorter time from first symptom to diagnosis compared to sporadic MS cases (2nd family member: Hazard Ratio (HR): 1.12, CI: 1.03–1.21, p = 0.007 adjusted: HR: 0.95 p = 0.22, CI 0.89-1-03 and 3rd family member HR: 1.64 CI: 1.22–2.20, p = 0.001 adjusted model: HR: 1.70, p-value: 0.000, CI: 1.32–2.18). The same difference was not seen between 1st family members and sporadic cases (HR: 1.05, CI: 0.98–1.13, p = 0.15, adjusted: 0.98, p-value: 0.53, CI: 0.91–1.05). Estimated marginal mean delay in the four groups were 4.60 years (95% CI: 4.11–5.01) in1st family members, 4.23 years (3.71–4.75) in 2nd family members, 2.11 years (0.95–3.26) in 3rd family members and 4.99 years (4.99–4.99) in sporadic MS cases. ConclusionThe 2nd and 3rd family members in MS families tend do get diagnosed faster than sporadic cases. This has implications in the diagnostic process of familial MS cases.

Reservoir characteristics and genetic differences between the second and fourth members of Sinian Dengying Formation in northern Sichuan Basin and its surrounding areas

Abstract This study investigated the characteristics and genesis of reservoirs in the 2nd and 4th members of Sinian Dengying Formation in northern Sichuan and its surrounding areas, on the basis of outcrop, drilling cores and thin section observation and geochemical analysis. The reservoirs of 2nd member are distributed in the middle part of the stratum. The reservoir quality is controlled by supergene karst and the distribution of mound-shoal complex. The bedded elongated isolated algal framework solution-cave and the residual “grape-lace” cave, which are partially filled with multi-stage dolosparite, constituted the main reservoir space of the 2nd member. There is no asphalt distribution in the pores. The pore connectivity is poor, and the porosity and permeability of the reservoir is relatively low. The reservoirs of 4th member were distributed in the upper and top part of the stratum. The reservoir quality is controlled by burial dissolution and the distribution of mound-shoal complex. The bedded algal framework solution-pores or caves, intercrystalline pores and intercrystalline dissolved pores constituted the main reservoir space of the 4th member. It's partially filled with asphalt and quartz, without any dolosparite fillings in the pores and caves. The pore connectivity is good. Most of the 4th member reservoirs had medium-low porosity and low permeability, and, locally, medium-high porosity and medium permeability. Affected by the development of mound-shoal complex and heterogeneous dissolution, the platform margin along Ningqiang, Guangyuan, Jiange and Langzhong is the most favorable region for reservoir development. Deep buried Dengying Formation in the guangyuan and langzhong areas should be the most important hydrocarbon target for the future exploration.

Quantitative fracture evaluation method based on core-image logging: A case study of Cretaceous Bashijiqike Formation in ks2 well area, Kuqa depression, Tarim Basin, NW China

A quantitative evaluation method of fracture is established based on core observation and image logging, and is used to characterize the distribution feature of fractures in Bashijiqike Formation of ks2 well area. This method gets the empirical corrections of fracture parameters between cores and image logging in the same depth, and these empirical values will be used in other depth where cores are not acquired to obtain all the fracture parameters per meter of the target layer. The study shows the fractures in ks2 well area are mainly high angle structural fractures between 45°−75°, and their strikes are near SN or near EW. The fracture linear density values are 0.11−1.30/m, the fracture area ratio is 0.027%−0.130%, the average fracture width is 0.13−0.55 mm, and the fracture length is 0.39−1.20 m. The development of fracture is divided into three levels (I-developed, II – relatively developed, III-poorly developed) based on the linear density value and surface area ratio. Fractures in this well area are most abundant in sandstones of 1st and 2nd members of Bashijiqike Formation, forming 4-6 fracture segments with good continuity. The thicknesses, development levels, parameters of fracture segments decrease exponentially with the increase of distance to fault and to anticline axis. The most favorable area (I – II) is within 800 m from the fault, or within 1 800 m from the anticlinal axis. It is predicted the fractures in ks2 well area, are more developed in the eastern area than the middle-western area, and more developed in the southern area than the northern area, and that the linear fracture density can be up to 1.0/m around Well ks201, Well ks207-ks2-12, Well ks203 and areas near faults.

Clinical phenotype in relation to the distance-to-index-patient in familial hypercholesterolemia

Background and aimWe evaluated whether the severity of the familial hypercholesterolemia (FH) phenotype, i.e. increased levels of low-density lipoprotein cholesterol (LDL-C) and cardiovascular disease (CVD) risk, decreases in more distantly related patients within one family. MethodsWe included heterozygous FH patients identified by genetic cascade screening in the Netherlands from 1994 to 2014. A cascade starts with identification of a genetically proven FH patient (“index patient”) followed by testing in first degree relatives. If a mutation carrier is identified, their first degree relatives are tested as well, and so on. The associations between distance-to-index (expressed as family relationship) and both LDL-C levels and CVD risk, were evaluated using multivariable linear and Cox regression models. ResultsDistance-to-index could be determined in 13,374 patients. Mean (±standard error) levels of LDL-C did not differ significantly in 1st, 2nd, 3rd, and 4th or more family members: 5.46 (1.42), 5.17 (1.42), 4.89 (1.37), and 4.58 (1.27) mmol/L, respectively (adjusted p-for-trend: 0.104). The adjusted hazard ratio of increasing distance-to-index for CVD was 0.92 (95% CI: 0.82–1.03). ConclusionThis study was the first to investigate the association between distance-to-index and the phenotype of a monogenetic disorder. The absence of a decrease of phenotype severity lends support for genetic cascade testing in FH.

Re-determining source faults of the Upper Cretaceous Putaohua oil layer in Sanzhao sag of Songliao Basin, NE China

Abstract From the deformation characteristics of two walls of a fault caused by fault activities, the activation of faults in the critical moment of oil and gas accumulation (structural inversion period) was analyzed to determine the source faults in the Upper Cretaceous Putaohua oil layer of the Sanzhao sag in Songliao Basin. Based on the previous classification and research results of activity patterns of the faults in the Sanzhao sag, the analysis of the structural deformation characteristics during the deposition of the 2nd and 3rd members of the Upper Cretaceous Nenjiang Formation and the inversion reveals that the feature of cutting to T 06 reflection layer (bottom interface of the third member of the Nenjiang Formation) can not be taken as the basis to judge whether the faults were activated during the inversion or not. But during the structural inversion period, the structural deformation caused by faults would lead to fault-propagation inverted folds and fault-bend inverted folds, which would further lead to obvious deformation differences between hanging walls and foot walls of faults, this can be taken as the basis to determine if the faults were activated or not in the inversion period, and then the source faults of the Putaohua oil layer can be determined. Furthermore the source faults can be divided into two kinds, concealed faults and penetrating faults, according to if the source faults cut through layers of inversion period or not. These two kinds of source faults show more obvious control over the planar oil distribution in the Putaohua layer than the previous study results.

Genesis mechanism of the Sinian-Cambrian reservoirs in the Anyue Gas Field, Sichuan Basin

The Lower Cambrian Longwangmiao Fm, the 4th and 2nd members of the Sinian Dengying Fm are the three major gas layers in the Anyue Gas Field of the Sichuan Basin. Their main characteristics and genesis mechanism were investigated, and the following three findings were obtained. First, according to sedimentary microfacies, lithology and porosity, the Longwangmiao Fm is identified as fractured-vuggy dolomite reservoir of grain shoal facies, the 4th member of the Dengying Fm as fractured-vuggy (cavernous) dolomite reservoir of cyanobacteria mound beach facies, and the 2nd member of the Dengying Fm as fractured-vuggy dolomite reservoirs of cyanobacteria mound beach facies. Second, the Longwangmiao Fm is mainly grain dolomite, with dissolution pores and vugs as major reservoir space, at an average porosity of 4.24% and an average thickness of 36 m. The 4th member of the Dengying Fm made up of cyanobacteria dolomite has dissolution pores, vugs and caverns as major reservoir space with an average porosity of 3.22% and an average thickness of 70 m. The 2nd member of the Dengying Fm composed of cyanobacteria dolomite has fractures and vugs as major reservoir space with an average porosity of 3.34% and an average thickness of 80 m. Third, those reservoirs experienced multiple evolutionary stages including porosity development, hydrothermal mineral filling, asphalt filling etc. Penecontemporaneous dissolution and supergene karstification are the key factors controlling the formation of the reservoir space and the evolution models of the reservoirs were figured out.

Geochemistry of the Sinian–Cambrian gas system in the Sichuan Basin, China

Based on the outcrops, core samples, drilling cuttings, seismic and geochemical data, natural gases of the Sinian–Cambrian gas system were derived from four sets of over-mature, high quality source rocks. The Cambrian Qiongzhusi source rock is sapropelic, with TOC of 1.94%, Ro eq. of 1.83–3.90% and a thickness of 140m on average. The Sinian (620–541Ma) Doushantuo source rock is sapropelic, with TOC of 1.69%, Ro eq. of 2.08–3.83% and a thickness of 11m on average. The 3rd member of the Dengying Fm. is also sapropelic, with TOC of 1.43%, Ro eq. of 3.16–3.21% and a thickness of 13m on average. The 2nd and 4th members of the Dengying Fm. are dominated by algal dolomite, with TOC of exhibiting 0.39%, Ro eq. of 1.97–3.46% and a thickness of 246m on average. Most of the δ13C2 values are lower than −28‰ and gas dryness is >99%, indicating that the natural gas is oil-derived with high maturity. The high contents of isoparaffins and cycloparaffin suggest that natural gas in the Sinian–Cambrian reservoir was originated from secondary oil cracking. The Cambrian Longwangmiao gas was mainly derived from the Cambrian Qiongzhusi source rock and the gas within the Sinian Dengying Formation mainly originated from the three Sinian source rock layers. The area with gas generation intensity superimposed the four sets of source rocks exceeding 6×109m3/km2 covered 80% of the Sichuan Basin. The proved reserves exceed 1.0×1012m3 in the Sinian–Cambrian gas system and the accumulated gas resource in the Sinian–Cambrian gas system might exceed 5×1012m3.

MEN1 gene mutations with different phenotypic presentations in two families: Is it a time to grade MEN1 mutations as high-risk and low-risk?

1540 Background: MEN1 syndrome results from MEN1 gene mutations and is characterized by primary hyperparathyroidism (PHPT), pancreatic endocrine tumors (PET), pituitary adenomas, thymic and other tumors. About 600 different mutations have been reported on Human Gene Mutation Database and 30 of them presented as Familial Isolated Hyperparathyroidism (FIHP); however, no genotype-phenotype correlations have been identified. Methods: We characterized 2 independent families with newly diagnosed MEN1. Mutation analyses were performed in Dept of Genetics Yale University. Diagnostic tests, surgical treatment were implemented. Results: Family 1 has 21 members. 5 presented with early onset of PHPT and no other tumors. 3 ½ parathyroidectomies were performed. A proband had direct sequencing that showed a mutation in Exon 7, consisting of single base insertion in codon 319 (TAC to TTAC)(c1065_1066insT). There were no deaths in the family. Family 2 has 20 members. 7 were tested and showed a mutation in Exon 2, consisting of single base deletion in codon 103 (CTG to _TG)(c417delC). One 1st generation member died from PET at age 79, three 3rd generation members had multifocal metatstatic malignant gastrinomas (ages 32, 39, 41). The proband had total pancreatectomy at age 32. Five members had PHPT, angiofibromas. Three 2nd generation members had thymic carcinomas (ages 20, 54, 60). Conclusions: Phenotypic presentation of MEN1 syndrome may vary with the same mutation suggesting a lack of genotype-phenotype correlation and the effect of modifying factors. On the other hand, these two families—one with a mutation predicted to truncate the menin protein close to its terminus and the other with a truncating mutation early in the coding sequence—have dramatically different severity of the syndrome. Our findings suggest that the exon 7 mutation has a milder effect on protein function resulting in FIHP. The management may be heavily influenced by the predicted clinical phenotype, we are proposing the development of a grading system for MEN1 gene mutations as low-risk and high-risk and to attempt to identify other modifying genetic and environmental factors to improve screening and timing for surgery.