Dynamic Reservoir Description On Gaotaizi Reservoir In Honggang Oilfield

Being at middle-later stage of development, Gaotaizi reservoir of HongGang oil field faces the difficulty of low oil production speed, water rising too quickly and low water drive recovery. This is because of the differences of petroleum accumulation and control mechanism in different oil groups and small layers, the differences of reservoir types and physical properties, the complexity of oil and gas distribution.In order to improve the development effect and enhance water drive recovery, it is necessary to carry out fine reservoir description, research on a dynamic model and remaining oil distribution modes is the most important.Geological modeling, seismic, well-log and production data were combined with Petroleum Geology, Tectonics, Logging Geology and Development Geology by using a research method of multi-discipline and multi-specialty. The research was divided into the following steps; the first step was to establish isochronal formation framework on the base of the fine isochronal stratigraphic division and correlation. The second step was to examine sedimentary microfacies, diagenetic facies and reservoir characteristics based on core observation. All of these were used to determine the type and distribution feature of sedimentary microfacies. Reservoir stochastic modeling was used to set up property models of different development stages under the control of diagenetic facies and sedimentary facies, combined with dynamic data. Based on the fine study on sandstone model and dynamic property model, combined with the reservoir flow unit and large pore research, the flow unit model of main exploitation stages and large pore model were made. This helped to analyse the type and distribution and development and evolution characteristics of flow unit and large pore. Evolution law was finally predicted. Finally, on the basis of previous research, according to dynamic data in different development and production period, dynamic fluid model was made, the evolution law of fluid found out, water-flood law and remaining oil distribution characteristics of each layer were known. It is useful to look for remaining oil enriched area and adopt potential tapping measures. Major results obtained in this study were as follows:(1) Based on combination of the tradition cycle-thickness correlation method and the high-resolution sequence stratigraphy, taking sandstone correlation model and the contacting of the strata into account, combining of geology, well-log and production data of the study area, and based on the precise correlation of marker beds and reference layer,224wells in the study area were finely divided and correlated. Three sand sets of Gaotaizi reservoir was divided into10oil layers and40small layers and65monolayers, the strata framework between wells were established and accomplished.(2) Based on analysis of7coring wells, according to its sedimentology characteristics, rock types, sedimentary structure, biometrics and rock facies, it was concluded that delta front subfacies and prodelta subfacies were deposited in the target intervals. On the basis of this, sedimentary microfacies of underwater distributory channel, mouth bar, deltal-fan front sheet sand, inter-distributory bay and prodelta mud were discerned in this area. Finally, the plane distribution maps of sedimentary microfacies of each monolayer as well as its spatial distribution model were given.(3) Through research on assay data of Qing2and Qing3member, it was showed that:the reservoir rock types were mainly lithic sandstone; few feldspathic lithic sandstone, lithoclastic quartz sandstone and lithic feldspathic sandstone. The compositional maturity was on low side and structural maturity was middle or slightly low; well-sorted; the psephicity was commonly assumed hypo-edge angle, cementation type was mainly pore cementation. Interstitial material was clay mineral which included kaolinite, illite, illite/smectite interstratified and chlorite. The reservoir pore type of target strata in study area was combined first by intergranular pore and intragranular corrosion pore, and next by mould pore and fracture with the reduced-neck, slim, sheet throat and cluster pore throat occurring as the main throat type. The pore structure was mainly medium pore and fine throat to fine pore and fine throat, which belonged to medium pore and lower permeability reservoir. (4) Based on analysis assay data, the diagenesis phase was divided into early A phase. Dissolved diagenetic facies and densification diagenetic facies were mainly diagenetic facies type of this area. The dissolved diagenetic facies which included intergranular dissolved pore facies were (â… ) porphyritic dissolved diagenetic facies (â…¡) constructive diagenetic facies; The densification diagenetic facies which included carbonate dense cementation diagenetic facies (â…¢) dense compaction diagenetic facies (â…£) destructive diagenetic facies. The logging response characteristics of diagenetic facies were studied and combined with well-log, and then the diagenetic facies models of the target stratum reservoir were given for the first time. Among the microfacies, underwater distributory channel mainly developed dissolved diagenetic facies and dense cementation diagenetic facies, mouth bar mainly developed porphyritic cementation diagenetic facies, and a variety of diagenetic facies could be found in sheet sand and distal bar. Generally speaking, destructive diagenetic facies had a relatively high proportion; dense compaction diagenetic facies were mainly developed in facies which were rich in mud.(5) Through analysis, the reservoir parameters database was acquired. Based on the research results of sedimentary reservoir and log data processing, application of petrel software and multifacies-controlled modeling method, the three-dimensional model of Gaotaizi reservoir in different development periods were given for the first time. This enabled quantitative characterization of various reservoir characteristics from the dynamic perspective. Reservoir physical property and dynamic changes of fluid were predicted, and the results shown as follows:single-period underwater distributory channel sand bodies had a high value areas of reservoir physical property, which was a favorable enrichment region of oil and gas; over-riding sand bodies of multi-period underwater distributory channel also had a high value areas of reservoir physical property. However, its heterogeneities were strong; reservoir physical property of mouth bar sand bodies was worse than that of the underwater distributory channel because of small scale and thinness of the sand bodies. The sand bodies which developed in constructive diagenetic facies could form enrichment region of oil and gas; the sand bodies of sheet sand and distal bar were thin, which could form better reservoir influenced by diagenesis.(6) According to the characteristics of Gaotaizi reservoir of Honggang oil field, selecting porosity, permeability, shale content, flowing interval index and R35as the analysis parameters, the reservoir flow units of this area was divided into4types. At the initial stage, â…£ class of flow units were widely distributed, â…  and â…¡ class of flow units were charact of ferized by a small range of extention, not discontinuous and well developed. However, â…¢ class of flow units were less developed. At well pattern infilling stage, â…£ class of flow units were even more widely distributed, â…  and â…¢ class of flow units were charact of increased area and continuous distribution. Water flooding could have an effect on the type and distribution of flow unit, the poor quality flow unit of initial stage could change into high quality flow unit, while the high quality flow unit of initial stage distributed more widely. In accordance with the practical production, it reflected the flow status of underground fluid.(7) Using the method and principle of stochastic modeling, the three-dimensional model of comprehensive index of large pore in major segment of different development periods was given. The development degree and distribution law of large pore were quantitatively predicted. It showed that comprehensive index of large pore in dominant flow units enlarged with the water injection time increased. It objectively reflected the change of reservoir large pore in water injection process. This then provided geological basis for the research on water drive efficiency and water injection program.(8) According to all kinds of three-dimensional models and dynamic development data, the moisture content distribution model of each monolayer year by year was made. The water distribution characteristics and water flooding laws of each layer were also predicted. The water flooding laws of this area were as follows:1) East-west fracture was the main type of large pore, which was also the major water flooding direction;2) The obvious effective response of oil well in every direction was observed in tectonic reverse parts;3) The injection-production relation was in accordance with the characteristics model of high permeable zone and the flow units model, but the correlation in sedimentary facies and injection-production relation was low.(9) Depending on strong or weak of injection-production relationship in study area, effective water injection policy was worked out. When the oil wells in well group is less than or equal to2, the injection-production relation was strong, injection to production ratio is0.7-0.9in the strong layer, in the medium layer is1.1, and in the weak layer is1.3-1.5. When the oil wells in well group is more than2, the injection-production relation was mainly strong and extra strong, mix-profile control or monolayer profile control was worked out in combination with output and injection-production directivity. The injection-production relation was mainly medium and weak, macroscopic water injection control was worked out in combination with output. Injection-production directivity and water injection modes such as low intensity short period, moderate intensity moderate period and high intensity high period. This indicated a very good result during production.(10) According to reservoir models of different development periods which was controlled by sedimentary facies and diagenetic facies, this paper described the characteristics and variation of reservoir from the dynamic perspective. It offered a better prediction for remaining oil distribution range, which is a newly-emerging research direction in reservoir description technology which has an important reference meaning to the development of similar reservoirs.