Font Size: a A A

Study On The Reservoir Geochemistry And Hydrocarbon Accumulation Laws Of Huqing Oil Field In Dongpu Depression

Posted on:2012-10-24Degree:DoctorType:Dissertation
Country:ChinaCandidate:Y X ZhangFull Text:PDF
GTID:1110330338468116Subject:Mineral prospecting and exploration
Abstract/Summary:PDF Full Text Request
In view of the problems existed in Huqing oil field of Dongpu depression, suchas oil source being unclear, systematic research on hydrocarbon migration,accumulation process and mechanism being insufficient, this paper summarizes thephysical properties and molecular geochemical features of the extract from sourcerock, oil and reservoir. Then, on this basis, it discusses hydrocarbon classification,oil/source relationship and oil-gas bearing system by using geological, well logging,analytical and chemical examination data as well as modern organic geochemistryanalysis. It also studies oil migration direction, hydrocarbon accumulation stage anddating, and hydrocarbon generation history through the technique of moleculargeochemistry, fluid potential analysis, fluid inclusion analysis and basin modeling. Atlast, this paper summarizes the hydrocarbon accumulation laws of Huqing oil fieldand brings forward the favorable exploration direction. The main achievements areintroduced as follows.(1) There are two sets of source rock in the Tertiary of Huqing oil field, Es1 andEs3, which are different from organic matter abundance, type and maturity. In Es1,the organic matter abundance is higher, with average organic carbon >1.0%, and thetype is I or II, but the evolution degree is lower in most area, being at animmaturity-low maturity stage. In Es3, the abundance is medium, and parent rock isdominated by transitional type. Most of the layers in Es3 are still at or have undergoneoil generation peak, and can be evaluated as good source rock. The biological markdistribution indicates that source rock in the study area was mainly formed in areducing environment of semi-saline to saline lake. Material source was dominated bythe mixture of aquatic life and continental higher plant. Source rock in Es3 is themajor oil source for present production in Huqing oil field, while in Es1 it contributes little to oil generation because of the low evolution degree.(2) The petroleum in Huqing oil field can be classified into three types based onits physical properties and group composition. Type I is of low density, low viscosityand light, dominantly distributed at the downthrow block of Changyuan, Xingzhuangfault and Liutun-Haitongji sag, with saturated hydrocarbon content higher than 70%.The oil is featured by highly saturated hydrocarbon, low nonhydrocarbon+asphaltenecontent and high maturity. Type II is of medium density and medium viscosity, mainlydistributed at the second step of Huzhuangji and Qingzuji. It is the major hydrocarbontype in Huqing oil field, with low oil maturity. Type III is high density, high viscosityand heavy oil, mainly distributed at the upthrow side of Xingzhuang and Shijiaji fault.Part of the oil has undergone biological degradation, with saturated hydrocarboncontent less than 50% and higher nonhydrocarbon+asphaltene content.(3) In oil source correlation, biological source of source rock, sedimentaryenvironment, maturity, etc. were selected as the factors to decide which indexes canbe effectively used for oil source relation study of Huqing oil field. The resultsshowed that oil accumulation was close to this oil field, generally distributed aroundthe sag. Oil maturity is higher in the middle of Es3, lower sub-interval of thedownthrow side of Changyuan fault, named block Hu41, and the downthrow side ofXingzhuang fault, named block Hu96. The oil was generated from the under sourcerock, and the reservoir can be considered as the pattern of self-generation andself-accumulation. Oil in Huzhuangji-Qingzuji second step was mainly from thesource rock in the middle of Es3 in Haitongji sag and second step itself, partly wastrapped from the southward migrating hydrocarbon from Liutun sag. Oil in blockHu19 of the upthrow side of Xingzhuang fault was mainly generated from lowmaturity source rock in Mazhai sag and was of low maturity. Taking Es32,3 salt as thedividing line, oil and gas bearing system was divided into two sub-systems, upsalt andsubsalt, based on source rock distribution, accumulation and cap composition, and oilsource correlation. The sub-system Es33,4 in subsalt was the major oil and gas bearingsystem, while Es1, Es2, Es31,2 in upsalt was the secondary.(4) Hydrocarbon migration direction in Huqing oil field was established by usingalkyl dibenzothiophene as oil-gas tracing parameter and combining with subsurfacefluid potential. The results showed that fluid potential is high near Liutun-Haitongjisag, while towards the slope belts it is relatively low. Sags are the main recharge areasand slope belts are the discharge areas. On the same surface, fluid potential is high atsoutheast and low at northwest. For the upsalt sub-system, the main hydrocarbon migration direction in Liutun sag is southward and northward, and the secondary iseastward and westward; while for Haitongji sag, northward and eastward is the mainmigrating direction, and westward, southward is the secondary, especially directiontowards the slope belt is only displayed at the north of the sag. For the subsaltsub-system, hydrocarbon occurred in Mazhai sag party migrated southward to blocHu19 and accumulated; hydrocarbon occurred in Liutun sag was obstructed by saltand could not migrate upward through fault, so the early-generated low maturityhydrocarbon migrated southward through communicated sand body, andlater-generated high maturity hydrocarbon was sealed by faults and accumulated inthe sags; second step in Hu-Qing area, especially at the north part, was party chargedby hydrocarbon from Haitongji sag, and partly by oil and gas occurred from thesource rock in second step itself. In Qingzuji area the hydrocarbon tended to migratefrom south to north. Later-generated high maturity oil and gas could be sealed by faultand accumulated around or in the sags.(5) The reservoir accumulation dating and stages of different belts in Huqing oilfield was decided by using fluid inclusion and basin modeling technique, as well asstratigraphic burial history and palaeo-geothermal history. The results showed thatfirst step had mainly undergone two-stage hydrocarbon charging process, the early in19~10Ma, and the late in 6~2Ma. Second step had undergone three-stage chargingprocess, the first occurring around 30Ma, the second in 19~7Ma, and the third mainlyfrom 4Ma. Third step was one-stage charging, occurring around 3Ma. By contrast, oilaccumulation in second step structure was relatively early, and from first step tosecond step and then to third step hydrocarbon charging tended to be late successivelyduring the same stage.(6) By the guiding of reservoir geochemistry theories, hydrocarbon accumulationof Huqing oil field was concluded into three patterns, self source- lateral migrationand accumulation of sand body, mixed source-lateral and vertical migration andaccumulation of sand body-fault, other source-lateral and vertical gradient migrationand accumulation of sand body-fault-unconformity. First step in Huqing oil field isdominated by the pattern of. The main pattern of second step is mixed source-lateraland vertical migration and accumulation of sand body-fault, and self source-lateralmigration and accumulation of sand body is the supplementary pattern, formingvarious and complicated reservoir, with the richest hydrocarbon reserves. The patternof third step is generally other source-lateral and vertical gradient migration andaccumulation of sand body-fault-unconformity, with unfavorable accumulating condition and low hydrocarbon enrichment. At last, hydrocarbon accumulating rulesof Huqing oil field were summarized, and favorable oil-gas exploration direction andpotential field was pointed out based on the above study.
Keywords/Search Tags:HuQing oil field, Geochemical features, Fluid inclusion, Fluidpotential, Hydrocarbon accumulation
PDF Full Text Request
Related items