Study On The Sedimentary Microfacies And Gas-water Distribution Law Of Hongtai Gas Field

Hongtai gas field is at the northern of Tuha basin which is in the eastern of the depression.It overall taking on the tectonic pattern o f two low-lying sandwiching two uplift. Meaning that the tectonic patte rn of the faulted structures and uplift belt of Hongtai-Qiketai, the fa ulted structures and uplift belt of Caonan,the north groove of Hongtai, the south groove of Hongtai. The anticlinal belts of hongtai is an asym metric anticlinal structure of northeast-trending,that is on the one h and the westnorth is wide and gentle, on the other hand the eastsouth i s steep. By taking into account of the reservoir formation, these anticl inal structures on the one hand can play the transportation role in mi grating the source rock,and on the other hand lead to favorable matchi ng relations among source rock, reservoir rock and cap strata.The mainly producing members of this research region are Qiketai,S anjianfang and Xishanyao formations of the Middle Jurassic, this thesis is relate to Sanjianfang formation(J2s) which is the mianly member of study area. It is conformable contact between sanjianfang formation an d lower strata Xishanyao formation.The formation can be divided into f ive lithologic members in ascending order:The lower segment is browni sh red, crimson mudstone and sandy mudstone, the partial of this area is mingled with greyish-green mudstone;The middle segment is French gray sandstone mingled with greyblack greyish-green mudstone and coal bed as well as greyblack carbargilite;The middle segment is brownish red,c rimson mudstone and sandy mudstone, the partial of this area is mingled with greyish-green mudstone. The upper segment is mainly include unequ al thickness alternate layer which is greyish-green mudstone、linen blo cklike sandy stone and siltstone.Sanjianfang formation is the major reservoir of Hongtai area, the south-north distribution braid river delta plain, braided river delt a front submersed channel sand body and mouth bar sand body reciprocal o verriding with gradually increases from west to east slope structural setting of hongtai area, which had built up redundant structural settin g lithologic gas reservoir. The reservoir sandy displayed the low ratio between sandstone and stratum thickness,the excessive variation in ve rtical develop, the fast variation in lateral, the bad connectedness in single sand and so on characters.During the research of Hongtai area, there are many kinds of strati graphic correlation methods could be taken for the situation of work a rea. Mainly include strata correlation method, equal-thickness correlati on method,sedimentary cycle equence method, sedimentary facies transiti on correlation method. In the study area it mainly adopt cycle-thicknes s correlation method. On the base of the detail analysises of seismic d ata, logging data, well logging data, drilling well and coring data and m any test data. The stratigraphic classification and correlation method have been used in the Middle Jurassic strata of Hongtai area. During st udy the process of depositional time unit correlation marker bed, which is the most reliable, precise method. So, in order to realize the big ar ea, multi-wells, fine unit, accurate, delicate correlation of the project, we must focus on searching, identify, confirm more marker bed.Through se eking and identifing the intended zone of Sanjianfan formation of the whole area, determined6steady marker beds and3steady reference lami nas.We taken the steady mudstone layer as contrastive mark, Sanjianfang formation was classified by carried out the order of cyclic sedimenta tion descond method and used the step control strata correlation theor y. Under the control of cyclic sedimentation and mark layer, Sanjianfang formation can be classified into five sandstone group (S1, S2, S3, S4, S5), among them S1, S3and s4can be partly subdivided into3sublayers. Th e stratigraphic classification and strata correlation method, The metho d not only displayed the isochronal stratigraphic units meaning, avoide d the sand body crossing seam, maked the work of stratigraphic classifi cation and strata correlation became rational, but also maintained the reliability on the condition of facies change horizontal correlation o f reservoir. As sedimentary microfacies mapping by taking isochronal st rata unit method, it real reflected microfacies feature differential ch aracteristics in isochrohal stratigraphic frame, and guaranteed the pre cise of rationality research.This is supplied a solid foundation for i ntimate understanding the bit-plane distribution feature of sublayer s edimentary microfacies in study area. Based on observing rock core and comprehensive log interpretation methods, redivision and recorrelation the individual layer;Though the theory of taken the steady mudstone la yer as contrastive mark, carried out the order by cyclic sedimentation descond and step control strata correlation, taken the fine stratigraph ic division and comparison of50wells in Sanjianfang formation reserv oir, which built up a fine monolayer model.The target zone of Sanjianfang formation in this area developed la ke transgression and regression for twice times, it can be divided into four sedimentary cycles, from bottom to top it performanced:the lake1evel rised, developed a set of foreshore-shallow lacustrine mudflat sed iment which amounting the s5sandy group; after that the lake level dr awdown, it deposited a set of sandy body,it is dominated in channel of braided fluvial facies sandstones and channel bar sedimentary which am ounting the s4sandy groups; and then the lake level drawdown again,it deveped a set of Braided Delta plain sedimentary sandy body,it is dom inated in channel of braided fluvial facies and channel bar sedimentar y. The marsh of floodland had developed. The whole foreset process is sh ore-shallow lake-the braided delta plain-the braided delta front-the braided delta plain.Generally speaking, from S4to S1have obvious characters of inherit ance, the consistency distribution of sandy body in this area, the narro w border and banded distribution of high energy channel. Confined effec tive reservoir lateral continuity. Hongtai Well area mainly included di stributary channel and underwater distributary channel microfacies fac ies belt, from s1to S2sandy groups are developed energetic piont bat m icrofacies of river channel, the S2and S4sandy groups mainly developed underwater distributary channel microfacies facies;The essential hydr ocarbon pore volume in this area was built by the distributary channel, piont bat and sandy stone of underwater distributary channel microfaci es facies. From observating the core of coring well, determining lithofa cie types and sedimentary microface types of work area, it provided a b asis for the distribution law of sedimentary microfaces.On the base of precise calibrated with seismic geological, which ca rried out fine interpretation of faults and the bottom of Qiketai form ation(Qd)、the bottom of S1sandy group in Sanjianfang format ion (S1)、th e bottom of S2sandy group in Sanjianfang formation (S2), the bottom of S3sandy group in Sanjianfang formation(S1), the bottom of S4sandy group in Sanjianfang formation(S4), the Bottom of S5sandy group in Sanjianfa ng formation in(S5)the work area. The results showed that the work area developed an arched structure and a monoclinal structure,existing5ma il faults and more than20smaller faults.These observations were used to determine the standard of litho-elec correlation,built up the lith o-elec switching model. Using manual interpretation method for the sin gle layer of single well sedimentary microface, built up single well lo ngitudinal phase sedimentary microface model.There are three kinds of hydrocarbon reservoirs in study area:the arch reservoir, the lithologic reservoir,the lithologic and fault reser voir. Hongtai gas reservoir is the typical condensate gas reservoir, the reservoir dominated fluvial sandbody of braided river delta. The Finer lithology, the thinner sand layer, the worse horizontal connection, the lengthwise direction multi-period fold, the mudstone interstratified be d abnormal development, the more form lithologic reservoir. So this area mianly developed reservior controlled by structural and lithologic do uble factors. On the top of the nosing uplift mainly formated by struc tural hydrocarbon reservoir, at the limb developed structural-lithologi c reservoir, adjusting by the faults, the main characteristics of hydroc arbon accumulation is along structural setting in step movement style. In conclusion, from deep to shallow, the distribution area is progressi ve increased of gas and oil, that is the hydrocarbon potential of the t op is better than the bottom. In the same layer the distribution of gas area bigger than the oil area, which concentrated distribution at the west-north limb lower location of the structure. On the whole, there is a composite reservoir controlled by the structural-lithologic in study area.Againsted tectonics setting,synthesized the attributions bound wit h oil and gas, after research three favorable zones and several specifi c targets were presented. Three favorable zones:that is the east target zone of HT202well, a set of target zone of HT205well and HT206well, the south-east target zone of HT601.Though the stratigraphic correlation, analysed the sedimentary syst em, combinated the structural feature research of study area, integrate utilized geophysical method, which predicted the sandy body and oil-gas, assessed perfect target area, proposed favorable exploration region, pro posed specific exploration target well.