Prediction Of Monosandstone And Design Of Horizontal Well In Fluvial Plain And Delta System

Fuyu reservoir is an important field of inereasing reserves and yield of Daqing Oilfield in northern Songliao Basin.After years of comprehensive study in petroleum geology,many difficulties still exist in exploration and development such as: difficult monosandstone prediction,complex oil layer distribution and low straight wells yield.In this paper,we followed the guidance of high-resolution sequence stratigraphy and fine sedimentology theory,took Fuyu reservoir of Southern Putaohua Oilfield as the subject of study,systematicly researched the study of high-resolution sequence stratigraphy division and correlation,microfacies and energy-facies,monosandstone prediction,model for controlling hydrocarbon accumulation and horizontal well design in fluvial plain and delta system.High-resolution sequence stratigraphy study shows that it can be identified as two types of medium-term base level cycle,three types and seven sub-types short-term base level cycle in Fuyu reservoir of Southern Putaohua Oilfield.FuyuⅠ,Ⅱformation can be divided into two long-term base level cycles,five medium-term base level cycles,twelve short-term base level cycles and twenty-six super short-term base level cycles.High-resolution sequence stratigraphic framework of monosandstone is established by using the method of isochronious stratigraphic correlation.The sedimentary characteristics of Fuyu reservoir are studied under the control of isochronous stratigraphic framework.It shows that fluvial facies and delta deposition is developed from bottom up to top of Fuyu reservoir.Five types of subfacies and seventeen types of microfacies of fluvial plain and delta system are identified,which can be subdivided into thirty-four types of energy-facies by analyzing the depositional hydrodynamics.On the base of this,the method of point-line-surface to describe monosandstone and hydrodynamic energy-facies is established.The distribution of microfacies and hydrodynamic energy-facies on the plane in twenty-six super short-term base level cycles is depicted.Fluvial plain and delta system sedimentary models of Fuyu reservoir in Southern Putaohua Oilfield is established by analyzing the control effect of base level cycle on the distribution and evolution of sedimentary microfacies and energy-facies.There are seven sedimentary models such as rising period of fluvial facies low accommodation space,duration period of fluvial facies low accommodation space,fluvial facies high accommodation space,off-coastal delta distributary plain,nearby coastal distributary plain,inshore inner front and offshore inner front.The study of monosandstone prediction shows that wavelet decomposition technique and spectrum inversion technique basing on wavelet side-lobe compression can be used to identify monosandstone which is shielded by wave peak and trough,near the zero phase below the trough of T2 phase axis as each section.Considering advantages of the plane continuity of seismic attributes and high vertical resolution of waveform indicator inversion,the monosandstone prediction method of well-seismic combination guided by high resolution sequence stratigraphy is put forward.The seismic attributes can be subdivided by waveform indicator inversion.The study has achieved the purpose of identifying the monosandstone distribution characteristics of Fuyu reservoir in Southern Putaohua Oilfield.The study of model for controlling hydrocarbon accumulation shows that the accumulation in monosandstone traps taking major channel sand body as favorable reservoir is covered by mudstone on the top and sheltered by lithology or fault in the upper dip direction.The main controlling factor of monosandstone reservoir is major channel sand body.Oil and gas accumulated in the major channel sand body which the porosity is more than 8% and the permeability is more than 0.2×10-3μm2.There are three types of trap identified such as composite fault-lithologic trap,composite structure-lithologic trap and lithologic dip cusp trap.Basing of this,the model of “fault(structure)-sedimentary microfacies controlling trap,major channel sand body controlling oil” is established in Fuyu reservoir of Southern Putaohua Oilfield.The method of tracking major channel sand body and the physical property cyclicity analyzing in monosandstone lithologic reservoir is put forward.The method predicts that the horst zone and fault-nose zone are favorable areas in Fuyu reservoir of Southern Putaohua Oilfield.Considering achievements in deposition,reservoir and reservoir controlling,the targeted layer for horizontal well is proposed.In the process of depicting the monosandstone of a horizontal well,basing on the anatomy of dense well network in the development area,the top structure and boundary of monosandstone can be depicted by predicting super short-term base level cycle and waveform indicator inversion.Taking monosandstone contour as control,we can characterize architecture of monosandstone by combining interlayer drilled and theoretical model.On base of these,the description method of “top surface and boundary-architecture” for horizontal well trajectories is established,which is step by step controlled by the depict of target monosandstone.There are 9 trajectories depicted.Isochronous stratigraphic correlation method of horizontal well is established by using geosteering technique.On the basis of the architecture,lithology and electrical characteristics of channel monosandstone,geological guidance method is proposed to control horizontal section drilling in the channel monosandstone.It effectively ensures horizontal wells entering target monosandstone and improves the drilling rate of sandstone in horizontal section.All of these above provide guidance for exploration and development of oilfield.