| Lake delta is one of the most important oil and gas reservoir of Chinese continental petroliferous basin, in which the sand body from front facies is the main reservoir occurrence position. Depending on the direction of the land-to-lake, sand body of front facies of Delta can be divided into two subfacies:outer delta front and inner frontal of delta.The outer delta front sand body has its own uniqueness in sedimentary position, sedimentary energy, water depth, etc. At present there is little research about this kind of sand body about the sedimentary characteristics, sand body internal structure characteristics, and dynamic development response law. Taking the Bidian district of Biyang sag in Nanxiang basin as an example, this thesis is based on the geological, seismic, core, well logging, testing and the actual dynamic development data and other basic material of the front delta to discuss the sequence stratigraphy and sedimentary characteristics and sedimentary system, sand body space combination structure and production dynamic response law. It is not only important for understanding of sedimentary characteristics and evolution of sand body, but also for sand body space combination style and features. It has a great significance for this kind of reservoir for oil and gas exploration and development.Based on the sequence stratigraphy, sedimentology, reservoir geology, logging geology, this thesis established the sequence stratigraphic framework of study area, refined the sedimentary facies, analysis of the vertical evolution law of sedimentary facies, and put forward the deposition model for delta front. On the basis of the formation characteristics and sedimentary characteristics, the thesis classified space combination style of the sand body of the delta front, advanced two kinds of sand body causes combination types of distribution mode:the aggradations type and retro gradation type. Combined with production data in Bidian district, study on the3D geological modeling and production dynamic response has been done. The achievements obtained can be summarized as the following.Through the application of analysis method of high resolution sequence stratigraphy by Cross this thesis constructs stratigraphic framework of third member of Hetaoyuan Formation. By using seismic data and geochemical elements analysis, core and logging data, we can identify nine seismic reflectors (SBH23, SBH3, SBH32, SBH33, SBH34, SBH35, SBH36, SBH37, and SBH38). These specific calibration horizons are:top interface of III pay zone of the second member of Hetaoyuan foramtion (SBH23), top interface of the third member of Hetaoyuan foramtion nuclear or top interface of I pay zone in HⅢ formation (SBH3), top interface of II pay zone of the third member of Hetaoyuan foramtion (SBH32), top interface of III pay zone of the third member of Hetaoyuan foramtion ((SBH33), top interface of IV pay zone of the third member of Hetaoyuan foramtion (SBH34), top interface of V pay zone of the third member of Hetaoyuan foramtion (SBH35), top interface of VI pay zone of the third member of Hetaoyuan foramtion (SBH36), top interface of Ⅶ pay zone of the third member of Hetaoyuan formation (SBH37), top interface of Ⅷ pay zone of the third member of Hetaoyuan foramtion (SBH38). Through the synthetic seismic records horizon fine calibration, this thesis made the well logging, seismic data harmonious and unified.According to theory of the high resolution sequence stratigraphy, and the hierarchy of the formation, this thesis divided the third member of Hetaoyuan Foramtion into long-term cycle, medium-term cycle and short-term cycle three orders, analyzed on the differences of characteristics in multi-order formation cycle, and divided study area into9long-term half cycle of basal level up or down,23middle of half cycle of basal level up or down and several short cycles.Based on the research of the location, distribution pattern of sand body and supply direction of different provenances, this thesis made all wells in different level of sequence stratigraphic division and correlation, which is divided into58thin layers and114single sand bodies.Depending on the development of sand body and analysis of heavy mineral material this thesis analyzed the characteristic of provenance in Bidian district, finding that Fuwan-Zhangchang and Gucheng in north is the main provenances, while Shuanghe in north and Wangji in northeast are the secondary provenances in study area.Using results from core observation and analysis of petrology characteristics, this thesis divided rock facies classification of Bidian district into four categories:pebbled sandstone rock facies, medium thick sandstone rock facies, silty sand rocks and mud shale rock facies, and explain structure characteristics and analyses the genesis for each rock facies. Under background of the macro sedimentary in Biyang sag, making full use of core, logging, well logging data, this thesis classified microfacies types of the delta, fan delta sedimentary. The delta front facies are fatherly subdivided into exo-front and external front subfacies, and inner front subfacies sedimentary microfacies include:subaqueous distributary channel, mouth bar and, the outer front subfacies sedimentary microfacies include:subaqueous distributary channel endings, far sand dam. Corresponding to fan delta sedimentary microfacies is respectively subaqueous distributary channel, between channels frontal sand, subaqueous distributary channel endings, sand sheet.From characteristics of the sediment grain size, logging facies, thickness of sedimentary sand body and different sedimentary microfacies types of lithology, sand body thickness, logging facies are analyzed. The thesis compared the deposition features of differences between inside and exo-front facies in the different sedimentary and proposed the phase boundary of exo-front and inside front facies of the delta and fan delta, and also pointed out the differences in lithology, constructions of the principle, the microfacies distribution of the delta front and inner front sedimentary sand bodyOn the basis of the micro facies classification, the thesis studied the distribution of the sedimentary facies in vertical and plane, analyzed evolution regularity of the sedimentary facies in vertical, and introduced different sediment source of the depositional model in Bidian district.With the physical properties testing data of core sample, this essay analyzed the physical differences of different sediment provenances, lithology and sedimentary microfacies. Considering from the sediment provenance, the property of Gucheng is best, whose average porosity is21.75%, and the average permeability is427.31X10-3μm2; the second are Shuanghe and Fuwan-Zhangchang provenances; Wangji provenance is the worst whose average porosity is16.93%, and the average permeability is197.33×10-3μm2. Considering from lithology,powder sandstone porosity is less than21%, and permeability is less than80×10-3μm2; fine sandstone porosity is concentrated in21-26%, and permeability is concentrated in80-350×10-3μm2; the sandstone porosity is concentrated in26-29%, permeability is concentrated in350-1600X10-3μm2; the porosity of coarse and gravel sandstone is more than29%, and permeability is more than1600×10-3μm2.From the sedimentary microfacies, the porosity of delta outer frontal sand body is less than23and permeability is less than200×10-3μm2; porosity of fan delta outer frontal sand body is less than24.5%and permeability is less than250×10-3μm2, which is slightly higher than the outer frontal sand body of delta.On the basis of microfacies classification, according to the sand body vertical superimposed relationship, this thesis classified inner and exo-front delta, and the genesis assembly types of internal sand body of exo-front delta. In the delta depositional system, types of genesis assembly of sand body are:underwater distributary channel and its endings, mouth bar peripheral combination of underwater distributary channel, underwater distributary channel and far sand dam, mouth bar and far sand dam, underwater distributary channel endings and far sand dam, far sand dam superposition combination. In the fan delta depositional system, types of combination cause about sand body are:underwater distributary channel, underwater distributary channel peripheral combination, frontal sand-underwater distributary channel peripheral combination, underwater distributary channel, sand sheet combination, frontal sand, sand sheet combination, underwater distributary channel endings-sand sheet combination, sand sheet superposition combination six types. Among them, the most common sand body combination type is the far sand dam superposition combination for delta and sand sheet superposition combination for fan delta.According to provenance supply and variation characteristics of lake level, this thesis proposed two kinds of distribution mode about genesis assembly of sand body in study area, namely progradation type and retrogradation type. Genesis assembly types of different sand bodies in Ⅶ oil formation,Ⅵ oil formation, Ⅴ oil formation, lower Ⅳ oil formation, lower Ⅲ oil formation and lower Ⅱ oil formation belong to retrogradation type, while which in upper Ⅳ oil formation, upper Ⅲ oil formation and upper Ⅱ oil formation mostly belong to progradation type.Through thickness of sedimentary sand body, drilling footage vertically, property rhythm rate, heterogeneity etc, this thesis discussed the features of different sand bodies combination, and found that the thickness of the sedimentary sand bodies in genesis assembly of channel-underwater distributary channel endings sand body and mouth bar-underwater distributary channel endings is the largest, and the vertical drilling footage is lower, heterogeneity is relatively weak.With minimum distribution range, the permeability rhythm city is likely negative-positive or positive-negative, which in study area is rare. On the contrary, the genesis assembly of overlying sand made of thin layer far sand dam (sand sheet) is totally different, and its permeability rhythm city is mostly symmetric composite.With the change of sandstone thickness and sandstone percentage, the development of sand body show different types. There are four types of sand body structure in the third member of Hetaoyuan formation in Bidian district such as stable channel thick layer, unstable river thick layer, stable sheet thin layer and unstable sheet thin layer. When the sandstone thickness is thicker than3m, sandstone percentage is higher than30%, the thickness of sand body which is supposed to be large with its good lateral connectivity can be considered as a kind of "stable channel thick layer" sand body structure. When the sandstone thickness is thicker than3m, sandstone percentage is lower than30%, the thickness of sand body which is supposed to be small with its bad lateral connectivity can be considered as a kind of "unstable channel thick layer" sand body structure. When the sandstone thickness is thinner than3m, sandstone percentage is lower than30%, the thickness of sand body which is supposed to be small with its bad lateral connectivity can be considered as a kind of "unstable sheet thin layer" sand body structure. When the sandstone thickness is thinner than3m, sandstone percentage is higher than30%, the thickness of sand body which is supposed to be small with its good lateral connectivity can be considered as a kind of "stable sheet thin layer" sand body structure.On basis of source distribution and sand body development of the main research formation in Bidian district, this paper sums up the three kinds of sand body structure3d model such as single source single channel, single source many branch channel and multiple source sand body structure model. The distribution of sand body structure of stable channel thick layer is often on the provenance direction, and mostly close to the provenance with large sand body thickness, high sandstone percentage, good horizontal and vertical connectivity, and relatively weak heterogeneity, which is developed in the delta front or internal and external front intersection area. The distribution of sand body structure of Unstable river thick layer is often on front underwater distributaries channel crotch, and mostly lenticular in isolation with bad horizontal and good vertical connectivity. The distribution of sand body structure of stable sheet thin layer is closer to land outside of the front delta with thin sheet presented sand body, good lateral connectivity and poor vertical connectivity; the distribution of sand body structure of unstable sheet thin layer is often in the provenance intersection area, which is away from the source and vertical source direction, with small sand body thickness, low sandstone percentage, poor lateral and vertical connectivity, which is often developed in the end of delta front or front delta area with stronger heterogeneity.Combined with the basic data of drilling, stratification, fault and so on, this thesis use Petrel modeling software to establish the structure model, the sedimentary facies model and physical property parameter model of Bidian district. In the process of establish model of physical parameters, this thesis choose the deterministic modeling and phased stochastic modeling. Through results, the phased stochastic modeling effect is better, while the simulation results high reliability in study area.Taking Bidian district as a example, the thesis does research on the existing production situation of the outer delta front reservoir. This thesis concludes that, the oiliness of sand body of the delta front is not so good, and the development effect is poor, productivity is low, composite water cut is rising fast, due to poor property.According to the actual production performance data, considering fluid producing strength, capacity evaluation and production decline analysis of genesis assembly types of different sand bodies, this thesis believe that the difference of sand bodies of different combination types in delta exo-front facies is obvious. The sedimentary sand bodies of mouth bar-underwater distributary channel endings and mouth bar-far sand dam combination types are thick whose property is good. In dynamic development process, its development effect is obviously better than that of overlying sand body in the far sand dam of which the fluid producing strength is relatively bigger, initial capacity is relatively higher, the time of stable production is relatively longer and the initial decline rate is relatively lower. |
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