Jinliang Zhang

Deposition and Diagenesis of Steep-Slope Glutenite Reservoirs: Shengtuo Field, Eastern China

This study deals with the diagenesis of steep-slope glutenites in the view of relationship between depositional facies and diagenetic alterations. The Lower Member of Shahejie glutenites sit along steep slopes of an intracontinental lacustrine basin, which is an important area of hydrocarbon exploration in eastern China. This kind of reservoir rocks can be divided into three major depositional environments: transgressive fan deltas, channelized sediment flows and fluxoturbidite fans. The glutenites are lithic arkose and feldspathic litharenite having an average composition of Q35F36R29, rich in metamorphic rock fragments. Diagenetic processes that have affected the glutenites include mechanical and chemical compaction, dissolution of detrital grains, and cementation by quartz overgrowths, calcite, ankerite, kaolin, illite, chlorite, and mixed-layer illite-smectite clays, as well as formation of minor zeolite, epsomite, halite, and glauberite. Considering glutenites in different depositional environments experiencing different diagenetic evolution pathways along the lacustrine basin margin, a schematic model was constructed to predict diagenetic conditions within the defined depositional facies. This study reveals that the spatial and temporal distribution of diagenetic alterations within depositional facies, and provides important insights to the controls on reservoir quality evolution. In addition, findings of the study are applicable to other continental steep-slope glutenite reservoirs of lacustrine basins.

Facies architectural analysis and three-dimensional modeling of Wen79 fault block, Wenliu oilfield, Dongpu depression, China

Wenliu oilfield is one of those typically structural reservoirs in Dongpu depression in China. Wen79 fault block is located in the south of Wenliu oilfield. Nowadays, it has entered the secondary oil recovery stage with a high water cut. Accumulated repository from long-term exploration and production makes the opportunity to fulfill a fine description of Wen79 fault block optimistic. Eight basic lithofacies types (Gt, St, Sp, Sl, Sh, Sr, Fl, Fm) were identified through core observation, and brief description and interpretation were given to each lithofacies. Assemblages of associated facies were arranged into four specified architectural elements (channel fill, proximal overbank, distal overbank, and shallow lake). For the purpose of quantified reservoir physical property characterization, a three-dimensional (3-D) architectural element model was firstly constructed by using the stochastic reservoir modeling technique, truncated Gaussian simulation (TGS). Subsequently, we used the sequential Gaussian simulation (SGS) method to capture probable distributions of reservoir porosity and permeability with the help of facies-controlled method. Meanwhile, non-facies-controlled physical property models were also built for a comparative study. Analysis of both kinds of models indicates that the facies-controlled physical property model is more reliable.

Diagenesis of braided fluvial sandstones and its implications for prediction of reservoir quality: a case study on the Neogene Shawan Formation, Junggar Basin, NW China

This study states the spatial and temporal distribution of diagenetic alterations and their influence on reservoir quality in the lower member of Shawan sandstones of the Chepaizi Uplift in the Junggar Basin, NW China. Sandstones in this unit, which contains heavy oil, are composed of mostly lithic arkose deposited in a braided fluvial environment. The diagenetic processes that have affected the sandstones include mechanical compaction, cementation by carbonates, quartz, and clay minerals, and dissolution of framework grains and cements. Relatively good reservoir quality of the studied arkosic heavy oil reservoir rocks deposited in the braided fluvial environment occurs when feldspar, lithic fragments, and calcite cement experience dissolution in channel lag sandstones. However, the pervasive distribution of early carbonate cements mainly concentrated in braid bar deposits has resulted in a great reduction of reservoir quality. This study reveals that understanding of diagenetic evolution of braided fluvial sediments is helpful for providing a better elucidation and prediction of reservoir quality, and the results of this study can be applied to guide the direction for exploration and production of heavy oil.

Sedimentary and sequence-stratigraphic characteristics of the lower second submember, Shahejie formation, M1 block, Wenmingzhai oilfield, Dongpu depression, China

AbstractsIt is favorable that the sequence-stratigraphic characteristic and sedimentology analysis of Paleogene and the associated deposits of Shahejie formation (FM.) be allowed a number of sedimentary evolution stages to be characterized and a sedimentary model of the lower second submember of Shahejie FM. (ES2) to be established. An integration of drilling, logging, testing, core descriptions, and high-resolution sequence stratigraphy has been used to provide a new conceptual depositional model for the M1 block; the results show that the lower ES2 is deposited as terminal fan, occurring in areas where sediment-laden waters decrease in size and vanish because of evaporation. The depositional model is composed of proximal subfacies, middle subfacies, and remote subfacies according to its lithology, electricity, and sedimentary structures. The combined analysis of lithological and sedimentary sequences has come to the conclusion that there are three levels of base level cycles and three kinds of interfacies for the lower ES2. The former includes fifth-order short-term cycle sequence (V), fourth-order medium-term cycle sequence (IV), and third-order long-term cycle sequence (III), respectively. The latter includes the scoured surface, the bedding change interface, and the thickness’ cyclic changing interface of sandstone and mudstone. The conclusion has been drawn that the lower ES2 of the M1 block is determined as a transgression process with increasing water depth based on the analysis and correlation of vertical stacking pattern.

Sedimentology and sequence stratigraphy of the second member of Shuangyang Formation, Y45 Block, Moliqing oilfield, Yitong Basin, China

AbstractsDetailed stratigraphic analysis of the second member of Shuangyang Formation of Y45 Block of the rift Yitong Basin in northeast China has revealed that the study area, previously interpreted as fan delta systems, actually originated mainly in relatively deep lacustrine setting with nearby line source. Two depositional systems have been recognized: slope apron and slump fan. The regional correlation of the lithofacies within the different depositional systems has led to a high-resolution stratigraphic framework of 20 small layers. Sequence boundary SB1 marks the top of the target interval and is characterized by thick and continuous mudstone overlying sand-rich lacustrine sediments. Sequence boundary SB2 marks the bottom of the target interval and is characterized by high-channel-ratio lacustrine deposits overlying stably distributed shales. Maximum flooding surface (MFS) marks the end of a transgressive tendency and the onset of a regressive tendency and is characterized by surrounding shale-rich zone. Two system tracts constitute the target interval together which is classified by SB1, SB2, and MFS. The base-level fluctuation has a strong tectonic component in accordance with the regional tectonic settings that during active subsidence stage, the base level rises rapidly and during relatively stable stage, the base level rises slowly and is usually overtaken by sediment supply rate.

Sedimentary characteristics of braided stream—braided fan of Shawan Formation in Chunfeng Oilfield, northwest margin of Junggar Basin, China

On the foundation of the geological background, textural maturity analysis, compositional maturity analysis, mudstone color index study, and other provenance research approach were fully made use of during this study to make certain the provenance of Shawan Formation in Chunfeng Oilfield. Provenance analysis of the Shawan Formation in Chunfeng Oilfield, conducted as the first stage of this study, revealed that the main provenance direction changed from northeast to northwest gradually, with a little fluctuation, while Shawan Formation was deposited. And then synthetically using seismic data, log data, and drilling data, according to petroleum geology and reservoir sedimentology, this study analyzed the sedimentary facies indicators, single-well facies, and logging facies in Shawan Formation; clarified the distribution of the sandbodies; and reached new insights on the types of the sedimentary facies of Shawan Formation in Chunfeng Oilfield. The research indicated that braided streams were developed during the deposition of the first member of Shawan formation and in the following two periods where braided fans became dominant little by little. These three microfacies, braided channel, channel bar, and braided plain, make up a typical stacked upward-fining cycle in the braided stream system. And the braided streams flowed from the northwest to the southeast in the research region, while the first member of Shawan Formation was formed. While the second member of Shawan Formation was deposited, the braided streams shrank gradually, and the braided fan coming from the northwest began to grow, with the flow direction moving from the northwest to the northeast. From the upstream to the downstream, the braided fan can be divided into three subfacies, proximal fan, middle fan, and distal fan. And when the third member of Shawan Formation was developed, the area of the braided fan became even larger than ever before, covering over almost the whole Chunfeng Oilfield.

A micro-spectroscopy system to measure UV-VIS spectra of single hydrocarbon inclusions

For measuring the UV-VIS spectra of single hydrocarbon inclusions, a new micro-spectroscopy system based on inverted microscope and reflective objective was established in this paper. This system includes a reflective objective, a micro-lens, a fiber cable, a 3D adaptor, a spectrometer and a common inverted microscope. The 3D adaptor was perfectly connected with the microscope and no need any rebuilding to the microscope. The reflective objective can be easily con-focused with the objective of the microscope. By the fiber cable, the micro-lens and the reflective objective, the external monochromatic light from the spectrometer was used to excite the inclusions. Using this system, we measured VIS spectra of the inclusions excited by the internal mercury lamp of the microscope. We also measured the spectra of the single inclusions excited by external monochromatic light source. In this case, the influence of the fluorescence of the grain around the inclusion was subtracted from the total spectrum. At the same time, the images of the inclusions were recorded by a CCD camera. Because this system has a low cost, stable and a high sensitive, it is promising to measure the fluorescence of micro-size samples.

Flow units classification for geostatisitical three-dimensional modeling of a non-marine sandstone reservoir: A case study from the Paleocene Funing Formation of the Gaoji Oilfield, east China

Abstract Flow units classification can be used in reservoir characterization. In addition, characterizing the reservoir interval into flow units is an effective way to simulate the reservoir. Paraflow units (PFUs), the second level of flow units, are used to estimate the spatial distribution of continental clastic reservoirs at the detailed reservoir description stage. In this study, we investigate a nonroutine methodology to predict the external and internal distribution of PFUs. The methodology outlined enables the classification of PFUs using sandstone core samples and log data. The relationships obtained between porosity, permeability and pore throat aperture radii (r35) values were established for core and log data obtained from 26 wells from the Funing Formation, Gaoji Oilfield, Subei Basin, China. The present study refines predicted PFUs at logged (0.125-m) intervals, whose scale is much smaller than routine methods. Meanwhile, three-dimensional models are built using sequential indicator simulation to characterize PFUs in wells. Four distinct PFUs are classified and located based on the statistical methodology of cluster analysis, and each PFU has different seepage ability. The results of this study demonstrate the obtained models are able to quantify reservoir heterogeneity. Due to different petrophysical characteristics and seepage ability, PFUs have a significant impact on the distribution of the remaining oil. Considering these allows a more accurate understanding of reservoir quality, especially within non-marine sandstone reservoirs.

Reservoir architecture and fracture characterization of low-permeability sandstone reservoir: a case study of Biandong oilfield, Jinhu depression, northern Jiangsu Basin, China

Fracture is one of the most important factors through the whole process of low-permeability reservoir development. Biandong oilfield is a typical low-permeability fractured sandstone reservoir, and has stepped into high water cut stage; thus, the waterflooding effect is poor. Therefore, many contradictions such as high moisture content, decreasing production speed, and low recovery efficiency are becoming increasingly prominent, which have seriously hindered the sustainable development, and need to be solved urgently. However, few such studies on reservoir characterization in low-permeability fractured sandstone reservoir have been conducted in China. In this study, through comprehensive analysis on reservoir characterization and sedimentary environment, significant results are achieved. Three types of fracture occurrence are identified; they are high-angle fracture, low-angle fracture, and horizontal fracture, respectively. Two types of reservoir pore (primary porosity and secondary porosity) are recognized based on thin-section observation and analysis. The diagenetic stage of Biandong oilfield are divided into three stages, early A, early B, and late A, respectively. Finally, a regional discrete fracture network model is established with Fisher’s algorithm based on three-dimensional geological model. All the research results presented above can make a significant instructing function for making reservoir development plan and improving recovery efficiency.

Identification of sedimentary facies with well logs: an indirect approach with multinomial logistic regression and artificial neural network

Taking K-successions of the H-Zone of the Pearl River Mouth Basin as a testing example, we used two kinds of approaches to implement the microfacies identification. One is a direct identification, the other is an indirect approach in which we conducted the lithofacies classification first and then identified the microfacies based on previously estimated lithofacies. Both approaches were trained and checked by interpretations of experienced geologists from real subsurface core data. Multinomial logistic regression (MLR) and artificial neural network (ANN) were used in these two approaches as classification algorithms. Cross-validations were implemented. The source data set was randomly divided into training subset and testing subset. Four models, namely, MLR_direct, ANN_direct, MLR_indirect, and ANN_indirect, were trained with the training subset. The result of the testing set shows that the direct approaches (MLR_direct and ANN_direct) perform relatively poor with a total accuracy around 75%. While the indirect approaches (MLR_indirect and ANN_indirect) perform much better with a total accuracy of around 89 and 82%, respectively. This indirect method is simple and reproducible, and it could lead to a robust way of analyzing sedimentary microfacies of horizontal wells with little core data or even are almost never cored while core data are available for nearby vertical wells.