Control of Facies and Potential on Jurassic Hydrocarbon Accumulation and Prediction of Favorable Targets in the Hinterland Region of the Junggar Basin

Exploration practices show that the Jurassic System in the hinterland region of the Junggar Basin has a low degree of exploration but huge potential, however the oil/gas accumulation rule is very complicated, and it is difficult to predict hydrocarbon-bearing properties. The research indicates that the oil and gas is controlled by structure facies belt and sedimentary system distribution macroscopically, and hydrocarbon-bearing properties of sand bodies are controlled by lithofacies and petrophysical facies microscopically. Controlled by ancient and current tectonic frameworks, most of the discovered oil and gas are distributed in the delta front sedimentary system of a palaeo-tectonic belt and an ancient slope belt. Subaqueous branch channels and estuary dams mainly with medium and fine sandstone are the main reservoirs and oil production layers, and sand bodies of high porosity and high permeability have good hydrocarbon-bearing properties; the facies controlling effect shows a reservoir controlling geologic model of relatively high porosity and permeability. The hydrocarbon distribution is also controlled by relatively low potential energy at the high points of local structure macroscopically, while most of the successful wells are distributed at the high points of local structure, and the hydrocarbon-bearing property is good at the place of relatively low potential energy; the hydrocarbon distribution is in close connection with faults, and the reservoirs near the fault in the region of relatively low pressure have good oil and gas shows; the distribution of lithologic reservoirs at the depression slope is controlled by the distribution of sand bodies at positions of relatively high porosity and permeability. The formation of the reservoir of the Jurassic in the Junggar Basin shows characteristics of favorable facies and low-potential coupling control, and among the currenffy discovered reservoirs and industrial hydrocarbon production wells, more than 90% are developed within the scope of facies- potential index FPI〉0.5, while the FPI and oil saturation of the discovered reservoir and unascertained traps have relatively good linear correlation. By establishing the relation model between hydrocarbon- bearing properties of traps and FPI, totally 43 favorable targets are predicted in four main target series of strata and mainly distributed in the Badaowan Formation and the Sangonghe Formation, and the most favorable targets include the north and east of the Shinan Sag, the middle and south of the Mobei Uplift, Cai-35 well area of the Cainan Oilfield, and North-74 well area of the Zhangbei fault-fold zone.

Control of facies/potential on hydrocarbon accumulation:a geological model for lacustrine rift basins

The formation and distribution of hydrocarbon accumulations are jointly controlled by ＂stratigraphic facies＂ and ＂fluid potential＂, which can be abbreviated in ＂control of facies/potential on hydrocarbon accumulation＂. Facies and potential control the time-space distribution of hydrocarbon accumulation macroscopically and the petroliferous characteristics of hydrocarbon accumulation microscopically. Tectonic facies and sedimentary facies control the time-space distribution. Lithofacies and petrophysical facies control the petroliferous characteristics. Favorable facies and high porosity and permeability control hydrocarbon accumulation in the lacustrine rift basins in China. Fluid potential is represented by the work required, which comprises the work against gravity, pressure, interfacial energy and kinetic energy. Hydrocarbon migration and accumulation are controlled by the joint action of multiple driving forces, and are characterized by accumulation in the area of low potential. At the structural high, low geopotential energy caused by buoyancy control anticlinal reservoir. The formation oflithological oil pool is controlled by low interfacial energy caused by capillary force. Low compressive energy caused by overpressure and faulting activity control the formation of the faulted- block reservoir. Low geopotential energy of the basin margin caused by buoyancy control stratigraphic reservoir. The statistics of a large number of oil reservoirs show that favorable facies and low potential control hydrocarbon accumulation in the rift basin, where over 85% of the discovered hydrocarbon accumulations are distributed in the trap with favorable facies and low potentials. The case study showed that the prediction of favorable areas by application of the near source-favorable facies-low potential accumulation model correlated well with over 90% of the discovered oil pools＇ distribution of the middle section of the third member of the Shahejie Formation in the Dongying Depression, Bohai Bay Basin.

Fine Single Channel Identification Controlled by Sedimentary Facies—Taking KLA Oilfield as an Example

The Neogene fluvial reservoir in the Bohai oilfield is one of the leading development horizons for increasing reserves and production in the Bohai oilfield. However, the development of offshore fluvial reservoirs is faced with the problems of thin reservoir thickness, narrow plane width, rapid lateral change, and thin well pattern. Taking the KLA oilfield as an example, this paper discusses the nuanced characterization and configuration of a single channel controlled by sedimentary facies to guide developing offshore river facies’ narrow channel main control oilfield. Firstly, based on a large number of core data, the acceptable sedimentary facies identification is realized, the sedimentary model of the study area is established, the delicate calibration of logging facies and seismic facies is realized under the constraint of the sedimentary model, and a set of technical methods for nuanced reservoir characterization guided by seismic sedimentology is summarized, to realize the boundary identification of composite channel configuration and further realize the nuanced characterization of the single narrow channel. Based on this set of technology, it guides the smooth implementation of horizontal wells in the oilfield. The drilling encounter rate of the reservoir in the horizontal section of the single well exceeds 90%, ensuring the injection production connectivity and increasing the reserve production rate by more than 10%.

Control of facies and fluid potential on hydrocarbon accumulation and prediction of favorable Silurian targets in the Tazhong Uplift,Tarim Basin,China

Exploration practices show that the Silurian hydrocarbon accumulation in the Tazhong Uplift is extremely complicated.Our research indicates that the oil and gas accumulation is controlled by favorable facies and low fluid potential.At the macro level,hydrocarbon distribution in this uplift is controlled by structural zones and sedimentary systems.At the micro level,oil occurrences are dominated by lithofacies and petrophysical facies.The control of facies is embodied in high porosity and permeability controlling hydrocarbon accumulation.Besides,the macro oil and gas distribution in the uplift is also influenced by the relatively low fluid potential at local highs,where most successful wells are located.These wells are also closely related to the adjacent fractures.Therefore,the Silurian hydrocarbon accumulation mechanism in the Tazhong Uplift can be described as follows.Induced by structures,the deep and overpressured fluids migrated through faults into the sand bodies with relatively low potential and high porosity and permeability.The released overpressure expelled the oil and gas into the normal-pressured zones,and the hydrocarbon was preserved by the overlying caprock of poorly compacted Carboniferous and Permian mudstones.Such a mechanism reflects favorable facies and low potential controlling hydrocarbon accumulation.Based on the statistical analysis of the reservoirs and commercial wells in the uplift,a relationship between oil-bearing property in traps and the facies-potential index was established,and a prediction of two favorable targets was made.

A method of seismic meme inversion and its application

Under the condition of thin interbeds with great lateral changes in terrestrial basins,a seismic meme inversion method is established based on the analysis of seismic sedimentology technology.The relationship between seismic waveform and high-frequency well logs is established through dynamic clustering of seismic waveform to improve the vertical and horizontal resolution of inversion results;meanwhile,by constructing the Bayesian inversion framework of different seismic facies,the real facies controlled inversion is realized.The forward model verification results show that the seismic meme inversion can realize precise prediction of 3 m thick thin interbeds,proving the rationality and high precision of the method.The application in the Daqing placanticline shows that the seismic meme inversion could identify 2 m thin interbeds,and the coincidence rates of inversion results and drilling data were more than 80%.The seismic meme inversion method can improve the accuracy of reservoir prediction and provides a useful mean for thin interbeds prediction in terrestrial basins.

Combination and distribution of reservoir space in complex carbonate rocks

This paper discusses the reservoir space in carbonate rocks in terms of types,combination features,distribution regularity,and controlling factors,based on core observations and tests of the North Truva Oilfield,Caspian Basin.According to the reservoir space combinations,carbonate reservoirs can be divided into four types,i.e.,pore,fracture-pore,pore-cavity-fracture,and pore-cavity.Formation and distribution of these reservoirs is strongly controlled by deposition,diagenesis,and tectonism.In evaporated platform and restricted platform facies,the reservoirs are predominately affected by meteoric fresh water leaching in the supergene-para-syngenetic period and by uplifting and erosion in the late stage,making both platform facies contain all the above-mentioned four types of reservoirs,with various pores,such as dissolved cavities and dissolved fractures,or structural fractures occasionally in favorable structural locations.In open platform facies,the reservoirs deposited continuously in deeper water,in an environment of alternative high-energy shoals（where pore-fracture-type reservoirs are dominant） and low-energy shoals（where pore reservoirs are dominant）.