Detail Characterization Study On Thin-Interbedded Reservoirs At High Water Cut Stage

PZ Oilfield is the only extra-large integrated oilfield with OOIP up to 1 billion tons in the Bohai Bay Basin,which is also the largest oil discovery offshore in China ever since,a strong support to oil production of Bohai Oilfield.This oilfield developed under the background of the basement uplift of Bonan low salient structures,locating in the Tanlu fault zone,belonging to huge anticline structures complicated by the faults,the poor quality of seismic data in local gas cloud areas resulted in multiple or non-unique interpretations in structures.The main oil-bearing strata is the Guantao and lower Minghuazhen Formation of Neogene,where sandstone and mudstone interactively developed longitudinally at high stacking pay thicknesses of 108 m on average and relatively dispersed,and the longitudinal gross thickness is large at 472 m on average.It has the typical features of thin interbedded reservoirs characterized by large quantity of sub-layers and highly heterogeneity.For long-term strong water flooding development with a set of layer series,it has entered the high water cut stage overall.Besides,resulting from the complex structure and the features of thin interbedded reservoirs,many development challenges are becoming increasingly prominent.Guided by the thinking of the detail reservoir description,based on the seismic reprocessing data and rich drilling data,fully combined with the regional structure deposition background,according to the recognition of the aspects of the formation frame,structure interpretation,deposition system etc.,we research on fine characterization of thin interbedded reservoirs at high water cut stage to conduct the study of the distribution rule of remaining oil,thus putting forward corresponding strategies for efficient exploration of oilfield.(1)Based on the regional tectonic analysis and high precision coherence technique,making full use of the rich dynamic and static data of the oil field,the strike-slip faults and their associated secondary faults in the gas cloud area are systematically characterized based on the analysis of fault systems of different orders and grades,in this way,the northeast strike-slip fault of PZ oilfield is defined as the main control fault in this area,and the recognition of tectonic fault model of this oilfield is also updated,which has been used for 15 years.(2)On the basis of the sediment source,integrated with all kinds of sedimentary facies marks,the sedimentary facies are newly understood and divided.By the analysis of the base level cycles and its accompanying change of accommodation space as well as the sedimentary evolution history,the whole sedimentary system of PZ Oilfield is built.It is believed that the Neogene Guantao Formation of PZ Oilfield is shallow braided river delta deposition,which is different from the previous understanding of fluvial facies deposition.(3)Based on the seismic processing data,the calibration accuracy of well-seismic and lithologic is improved by means of the reconstructing technique.On this basic,the prediction of reservoir distribution under the level of sand groups are achieved for the first time in PZ Oilfield by “the reservoir prediction technique based on well-seismic combination”.In combination with the reservoir sedimentary model,single sand body is mapped,and furtherly,"dynamic evolution process analysis" is used as the core technology to carry out the anatomy study of internal structure of sand body,and the refined three-dimensional geological model characterization is realized through multi-level modeling and differentiated model fusion technique.Detail interpretation of structural features,recognition of sedimentary system,fine depiction and characterization of reservoirs were conducted,together with an in-depth analysis of the remaining oil distribution.The detail oil distribution pattern for such thin-interbedded reservoirs at high water cut stage is established with stacked dedicated development patterns proposed,which includes the subdivisions of commingled layer series,complete injection-production well patterns on the plane,and producing some local remaining oils preferably with horizontal wells.After nearly three years application and real-field scale practice,the water flooding development effect in PZ Oilfield has been significantly improved.