Reservoir Prediction Research Articles

Field Research and Application of Tracking Adjustment Technology While Drilling for a Horizontal Well in Block A

A reservoir in Block A of an oil field is a new layer series in the new area, and a horizontal well has been deployed for the first time around the development of the target layer in the third section of the reservoir. Compared with the oil layers in the old area, the structure of the target layer in Block A is more complex, the reservoir changes rapidly, the prediction of sand-laden mud reservoir is difficult, and the tracking adjustment of horizontal wells while drilling is difficult. In view of the above problems, in order to ensure the drilling effect, we have carried out the basic geological research of the combination of well and earthquake, carried out the study of the correlation between rock and electricity and the combination of well and earthquake, carried out the multi-technology combination, innovatively formed the supporting technical methods of fine fault, micro-amplitude structure identification and reservoir prediction, established the fine three-dimensional geological model, optimized the well location and trajectory optimization design of favorable blocks, According to the technical process of “making plans before drilling, timely adjustment during drilling, and re-recognition after drilling”, 7 horizontal wells have been tracked and adjusted while drilling, with an average oil reservoir drilling rate of 85.3%, which has achieved good drilling results and increased geological reserves and productivity.

Fluid mobility calculation based on improved window parameters optimized S-transform for reservoir delineation

Time-frequency analysis is an important tool for seismic signal analysis and time-frequency resolution is the key to high-precision reservoir prediction. The time-frequency method of conventional S-transform is difficult to meet the requirements of high precision reservoir prediction at present. In this paper, an improved window-parameter optimization S-transform (IWPOST) method is proposed. In the IWPOST method, the scale parameters of the window function can be adaptively obtained according to the amplitude spectrum of the actual signal, and a new optimization adjustment parameter is introduced to further improve the window parameters. The comparison analysis of the synthetic signals shows that the IWPOST method has better time-frequency aggregation and can maintain high resolution at both high-frequency and low-frequency. Finally, the proposed method is used to extract the reservoir fluid mobility attribute from the real seismic data and the results indicate that the fluid mobility has a higher time resolution and exhibits better performance for reservoir delineation. The proposed method is conducive to delineate the reservoir range and provides reference for the exploration and development of the oil and gas reservoirs in this area.

Reservoir Characteristics and Favorable Area Prediction of Chang-6 Reservoir in Zhouguan Area, Ordos Basin

Reservoir Characteristics and Favorable Area Prediction of Chang-6 Reservoir in Zhouguan Area, Ordos Basin

Fracture prediction of tight sandstone reservoirs using outcrops and log curve-based extremum method: A case study of the Chang 7 Member of the Yanchang Formation in Block X, Ordos Basin

The lack of seismic data and special log data on the Chang 7 Member of the Yanchang Formation in Block X of the Ordos Basin poses a major challenge to the study of the development characteristics and identification of fractures that greatly influence on-site production. To overcome this obstacle, this study determined the macroscopic characteristics of fractures in the study area based on field outcrop profiles and indoor core observations. The results are as follows: (1) Fractures in the study area are dominated by regional fractures in weakly deformed structural areas, with three sets of fractures mainly occurring. Core observations show that fractures in the study area have high dip angles, small extensions, and small openings; (2) The vertical extended lengths of these fractures are significantly controlled by rock mechanical layers; (3) Fractures show three types of extended morphologies when meeting weak planes. Vertically, there is an exponential correlation between the sand body thickness and the fracture linear density. The argillaceous shale thickness has a logarithmic relationship to the fracture linear density when it is < 1 m and has an exponential relationship to the latter otherwise. The planar distribution of fractures is significantly affected by layer thickness and rock mechanical properties. Given the stable occurrence, high dip angles, and small extensions of regional fractures, this study highlighted the abnormal increase or decrease in log curve values of fracture segments by calculating the extrema of log curves. The purpose is to identify the locations and quantity of fractures using conventional log curves in the case of limited drilling data. This log curve-based extremum method enjoys a high resolution. For both coring and non-coring wells in the study area, there is a positive correlation between their fracture linear density determined based on the production segment thickness of vertical wells and their daily liquid yield in the first week of well test and pilot production. This result indicates that the method for identifying natural fractures proposed in this study is highly reliable. Moreover, this study provides key parameter controls for predicting the three-dimensional distribution of fractures. The understanding of the fracture spatial distribution is also a key external factor that affects the design and construction of horizontal well fracturing.

Study on stress sensitivity of bedding fractures and sand-filled fractures in shale oil reservoirs

Shale oil reservoirs are characterized by low porosity and ultra-low permeability, and hydraulic fracturing technology is needed to realize industrial oil flow. The sand-filled fractures formed in the shale fracturing process and the bedding fractures developed in the reservoir itself interact to form a shale oil fracture network system, which is the main migration channel for shale oil production. Studies have shown that the higher the degree of fracture development, the stronger the stress sensitivity of the reservoir, and the stress sensitive damage is an important factor that causes the decline of reservoir seepage capacity during shale oil production. In this paper, based on the shale samples in the Jiyang Depression, the flow capacity experiments of bedding fractures and sand-filled fractures were carried out to analyze the stress sensitivity characteristics of shale bedding fractures and sand-filled fractures, and to clarify the seepage capacity decline mechanism of complex fractures in shale. Provide experimental data and theoretical support for productivity prediction of block shale reservoirs after fracturing.

An Effective Thin Reservoir Identification Method for Fine Oilfield Development

Thin reservoirs prediction method such as spectral inversion has drawn considerable attention in recent years. In order to avoid extracting wavelets within the whole field area purposeless and to make the filtered data has preferable fidelity as well as signal-to-noise ratio, an effective structural constrained thin reservoir description method which combines spectral inversion and wide-band Ricker wavelet filtering technology has been proposed in this paper. The method given here is more credible and is suitable for the prediction of middle-deep thin reservoirs. We take LD-A structure within Bohai Bay Basin as an example to show the implement of our method. Several sets of thin sand layers which are hardly to recognize originally have been finally identified. Also, with the application of this method, a high-production thin reservoir of LD-B structure has been identified accurately, which provides credible information for subsequent fine oil exploration and development.

Study on tight reservoir law and prediction of favorable areas - Take Wangjiawan well block Wang 107 as an example

When the development of oil field continues, the production efficiency of the whole oil well will decline significantly. It is of importance to analyze the geological factors related to the reservoir storage law in order to re recognize the current status of the oil well and extract more resources from the oil well. This paper expounds that at the stage of oilfield development, the research on reservoir characteristics, reservoir sedimentary facies and reservoir characteristics and laws are discussed in depth and comprehensively, and the prediction of favorable areas of the oilfield is studied, which has brought corresponding references to oilfield staff. For the late stage of oilfield development, we should carry out fine geological research, determine the geological type, provide the best data base for improving the development plan of the reservoir, and carry out scientific analysis and research to improve the productivity of the late stage of reservoir development, so as to achieve the expected production efficiency.

Direct Exact Nonlinear Broadband Seismic Amplitude Variations With Offset Inversion for Young’s Modulus

Young’s modulus and the Poisson ratio are critical for shale reservoir identification, and oil and natural gas detection since they are elastic parameters that can reflect the fracturing properties of subsurface rocks. The broadband inversion approach can make full use of the seismic ultralow-frequency information by combining it with the inversion results in the complex frequency domain. This plays an important role in the stability and reliability of the inversion, improving its resolution. Nevertheless, at present, the amplitude variation with offset (AVO) inversions of these parameters is mostly in the form of linear approximations, and there are few inversion methods of exact nonlinear equations or broadband. Considering that the nonlinear equation of reflection coefficient compared with the linear approximation has higher precision and fewer assumption conditions, and the low-frequency information of the complex frequency-domain inversion can improve the reliability of the inversion results, we derive an exact reflection coefficient equation for Young’s modulus, the Poisson ratio coefficient, and the density based on the exact Zoeppritz equation and apply it to the broadband complex domain nonlinear prestack inversion. Young’s modulus and the Poisson ratio coefficients estimated by the new inversion method provide a theoretical basis for evaluating the reservoir brittleness and compressibility, as well as a new approach for shale gas reservoir prediction and sweet spot identification. We tested the accuracy and rationality of this method with both synthetic and field data examples.

Frequency-Dependent AVO Inversion and Application on Tight Sandstone Gas Reservoir Prediction Using Deep Neural Network

Frequency-Dependent AVO Inversion and Application on Tight Sandstone Gas Reservoir Prediction Using Deep Neural Network

Hilbert–Huang Transform Incorporating Analytical Mode Decomposition and Its Application in Fractured-Vuggy Carbonate Reservoir Prediction

High-precision time-frequency (TF) analysis (TFA) can accurately detect anomalies in oil and gas reservoirs. However, conventional TFA methods cannot effectively identify fractured-vuggy carbonate reservoirs, which are deep and strongly heterogeneous. In this paper, a TFA method based on analytical mode decomposition (AMD) and the Hilbert-Huang transform (HHT) is proposed. Specifically, seismic signals are decomposed by empirical mode decomposition (EMD) and then by AMD. Finally, the TF distribution of the seismic signals is obtained after Hilbert spectrum analysis (HSA). Synthetic seismic data demonstrate that the AMD-HHT method can effectively eliminate mode mixing and provide higher time and frequency resolutions and energy focus than conventional TFA methods. In addition, model and field seismic data also verify that the AMD-HHT method can effectively detect hydrocarbon-related energy anomalies hidden in broadband seismic data.

Research on infill adjustment method for XX narrow and thin sand body oilfield

The sedimentation of XX oilfield is mainly composed of underwater distributary channel sedimentation, and the sand body has the characteristics of “narrow, thin, and scattered”. Although basic well network development, primary and local secondary infill, edge expansion adjustment, and corresponding injection production relationship adjustments have been carried out, there are still problems in current development, such as poor well network adaptability, low utilization degree of thin and poor layers, fast production decline rate, long shut-in wells, and many inefficient wells. In order to explore the potential of infill adjustment in narrow and thin sand body oilfields and further improve oilfield recovery efficiency, well pattern infill adjustment work has been carried out, achieving good results. A supporting infill adjustment technology has been formed, which includes “well seismic joint fine reservoir prediction, multi-disciplinary research on remaining oil quantification, multi-parameter evaluation of infill well location optimization, and multi information fusion perforation layer optimization”, effectively improving the development effect.

Genetic mechanism of multi-scale sedimentary cycles and their impacts on shale-oil distribution in Permian Lucaogou Formation, Jimusar Sag, Junggar Basin

Complex lithofacies of Lucaogou Formation in Jimusar Sag promote strong heterogeneity of oil distribution in fine grained sedimentary rocks. It is of great significance to define the formation mechanism of fine-grained sedimentary rocks for favorable reservoir prediction and exploration target selection in Jimusar Sag. Based on detailed petrographic characterization, in-situ geochemical parameter testing, and high-resolution cycle analysis, sedimentary cycles on the micron to meter scales were successfully identified in Lucaogou Formation from Jimusar Sag. Precession-forced paleo-environmental evolution mainly induces the deposition of meter-scale sedimentary cycles. In the period of low precession, the paleo-environment is cold and dry, the lake level falls. Silt-grained particles advance toward the center of the lake basin carried by gravity current, thus siliciclastic sediments are mainly deposited. In the period of high precession, the climate is warm and humid, the lake level rises. The inputs of siliciclastic sediments are limited and the temperature increases, which are conductive to the carbonate deposition. On this basis, high-frequency paleo-environmental evolution caused by solar activity (70–110yr cycle) further induces the formation of sedimentary cycles on micron-centimeter scale. When the precession is low, the rise and fall of lake level controlled by solar activity is contribute to the deposition of tuff-rich lamina and silt-grained felsic lamina, respectively. The period of high precession is under the background of overall high lake-level, the rise and fall of lake level, along with fall and rise of temperature, controlled by solar activity finally induce the deposition of tuff-rich lamina and carbonate lamina, respectively. The development of multi-scale sedimentary cycles controlled by Milankovitch cycle and solar activity cycle have important implications for shale oil enrichment. The fine-grained sediments deposited during the period of low precession and intense solar activity dominate feldspar dissolution pores and intergranular pores, which are favorable for shale oil enrichment.

Direct hydrocarbon identification in shale oil reservoirs using fluid dispersion attribute based on an extended frequency-dependent seismic inversion scheme

The identification of hydrocarbons using seismic methods is critical in the prediction of shale oil reservoirs. However, delineating shales of high oil saturation is challenging owing to the similarity in the elastic properties of oil- and water-bearing shales. The complexity of the organic matter properties associated with kerogen and hydrocarbon further complicates the characterization of shale oil reservoirs using seismic methods. Nevertheless, the inelastic shale properties associated with oil saturation can enable the utilization of velocity dispersion for hydrocarbon identification in shales. In this study, a seismic inversion scheme based on the fluid dispersion attribute was proposed for the estimation of hydrocarbon enrichment. In the proposed approach, the conventional frequency-dependent inversion scheme was extended by incorporating the PP-wave reflection coefficient presented in terms of the effective fluid bulk modulus. A rock physics model for shale oil reservoirs was constructed to describe the relationship between hydrocarbon saturation and shale inelasticity. According to the modeling results, the hydrocarbon sensitivity of the frequency-dependent effective fluid bulk modulus is superior to the traditional compressional wave velocity dispersion of shales. Quantitative analysis of the inversion results based on synthetics also reveals that the proposed approach identifies the oil saturation and related hydrocarbon enrichment better than the above-mentioned conventional approach. Meanwhile, in real data applications, actual drilling results validate the superiority of the proposed fluid dispersion attribute as a useful hydrocarbon indicator in shale oil reservoirs.

Quantitative characterization of deep fault-karst carbonate reservoirs: A case study of the Yuejin block in the Tahe oilfield

The Ordovician reservoirs in the Tahe oilfield are dominated by fractured-vuggy carbonate reservoirs, of which fault-karst reservoirs are a hot topic in recent years. Fault-karst reservoirs feature high production, large burial depth, and strong heterogeneity under the control of faulting and karstification. Based on geological, logging, and seismic data, this study classified the Ordovician fault-karst reservoirs in the Yuejin block of the Tahe oilfield into three types, namely karst-cave, dissolved-vug, and fractured types, and established the integrated identification criteria of the three types of reservoirs. This study characterized karst caves, dissolved vugs, and multi-scale faults through seismic wave impedance inversion and frequency-domain detection of multi-scale faults. 3D geological models of different types of reservoirs were built using the combined deterministic and stochastic methods and characterized the spatial distribution of multi-scale faults, karst caves, dissolved vugs, and physical property parameters of reservoir. This study established the method for the geological modeling of fault-karst reservoirs, achieved the quantitative characterization and revealed the heterogeneity of fault-karst reservoirs. The karst-cave and dissolved-vug types are high in porosity and act as reservoirs, while the fractured type is high in permeability and act as flow pathway. This study lays the foundation for the development index prediction, well emplacement, and efficient development of the fault-karst carbonate reservoirs.

Quantitative characterization of volcanic expansion fractures based on thermodynamic coupling analysis

In recent years, volcanic reservoirs in the Bohai Sea have become the focus of oil and gas exploration and development. Volcanic activity during the Cenozoic provided favorable conditions for the development of hydrocarbon traps. These volcanics also result in difficulties during the drilling and development of oil and gas fields. Furthermore, the high-temperature magma induced thermal expansion in the surrounding rocks, which changed the local stress field and affected the fracture distribution characteristics of the surrounding strata. The complexity of the fracture distribution makes predicting lost circulation difficult and causes substantial economic losses. Therefore, it is necessary to characterize the volcanic perimeter expansion-type fractures effectively. The distribution of volcanic rocks is identified through logging and seismic data, with perimeter fracture development characteristics being analyzed. The temperature conditions of the volcanic activity were determined through core mineral analysis and thin section observation. Based on the laws of energy conservation and geomechanics, the principle of thermal coupling was applied to quantitatively predict the thermal expansion fractures caused by volcanic activity using a finite element numerical simulation method. To determine the extent of volcanic influence on lost circulation, and the development characteristics of fractures under the influence of these rocks were analyzed. The results provide an important reference for drilling and volcanic reservoir prediction in the Bohai Basin and guide for elsewhere.

Seismic inversion with L2,0-norm joint-sparse constraint on multi-trace impedance model

Impedance inversion of post-stack seismic data is a key technology in reservoir prediction and characterization. Compared to the common used single-trace impedance inversion, multi-trace impedance simultaneous inversion has many advantages. For example, it can take lateral regularization constraint to improve the lateral stability and resolution. We propose to use the L2,0-norm of multi-trace impedance model as a regularization constraint in multi-trace impedance inversion in this paper. L2,0-norm is a joint-sparse measure, which can not only measure the conventional vertical sparsity with L0-norm in vertical direction, but also measure the lateral continuity with L2-norm in lateral direction. Then, we use a split Bregman iteration strategy to solve the L2,0-norm joint-sparse constrained objective function. Next, we use a 2D numerical model and a real seismic data section to test the efficacy of the proposed method. The results show that the inverted impedance from the L2,0-norm constraint inversion has higher lateral stability and resolution compared to the inverted impedance from the conventional sparse constraint impedance inversion.

Geometry analysis and oil reservoirs prediction in the Lower Cretaceous clinoforms of the northern Priobskoye field

. Developing of the exploration criteria for oil reservoirs and non-structural traps in the clinoform successions are the key target as for detailed field appraisal in the West-Siberia basin well as for exploration in the clinoform complexes in the new sedimentary basins without drilling. Based on complex analysis of the seismic, well logs, well tests and core data in the northern Priobskoye field, the correlation between clinoform geometry, edge trajectory and distribution pattern of the reservoirs in the productive formation AS is established. The highest flow rates and reservoir properties are typical for bar deposits, proximal fan and slope channels. Deposits of bars are formed at the high stand system tract and at the beginning of the falling system tract on the edges of tangential clinoforms with gently ascending, flat and descending edge trajectory. Deposits of basin floor fans and slope channels are confined to the drop in the relative sea level and its low stand; it is advisable to search for them at the bottomset of tangential clinoforms with a descending edge trajectory and in gently cross-bedded clinoforms.

Pore throat heterogeneity of different lithofacies and diagenetic effects in gravelly braided river deposits: Implications for understanding the formation process of high-quality reservoirs

Tight gas sandstone is a unique kind of unconventional hydrocarbon resource in that its intricate pore throat structure governs reservoir physical properties and gas reservoir productivity. However, the effect of differential diagenesis of various lithofacies on the heterogeneity of pore throat structure remains unclear. In this paper, a series of experiments were integrated to evaluate pore throat structures and fractal characteristics of the different lithofacies in a tight sandstone gas reservoir, and followed by a study of the impact of diagenetic alteration on them. Results demonstrate that the mineral composition, dominant pore types, pore throat structural parameters, fractal dimension, and physical properties of various lithofacies are notably different, which is mostly attributable to diagenetic alteration variability. There are more primary pores and less clay mineral content in coarser lithofacies. Pebbly coarse-grained sandstone and sandy conglomerate reservoirs that have undergone strong dissolution have more composite pores composed of residual intergranular pores and dissolution pores, which help to form a homogeneous pore throat system with good connectivity, resulting in the best reservoir quality. Due to the strong compaction and high clay mineral content filling pores and throats in medium-grained sandstone and fine-grained sandstone lithofacies, a large number of primary pores were lost, and throats were blocked, which easily formed intercrystalline pores, leading to poor reservoir quality. Coarse-grained sandstone reservoirs with moderate clay mineral content have undergone moderate compaction and dissolution and have moderate reservoir quality. Filamentous illite is the most destructive clay mineral to pore throat connectivity. Intergranular dissolution pores and moldic pores contribute significantly to the physical properties of pebbly coarse-grained sandstone and sandy conglomerate reservoirs. Pebbly coarse-grained sandstone and sandy conglomerate lithofacies are considered high-quality reservoirs with greater development potential for tight gas. This work has important guiding significance for the prediction of high-quality reservoirs in similar tight sandstone reservoirs.

Parameter prediction of oilfield gathering station reservoir based on feature selection and long short-term memory network

As an essential part of the oil industry chain, oilfield united station needs the modeling and prediction of production parameters to avoid potential risks. In this study, the oil transfer temperature of an oilfield united station in China is modeled using long and short-term memory network (LSTM) with feature selection to attenuate “curse of dimensionality“, including spearman's rank correlation coefficient-LSTM(SRCC-LSTM), R-type clustering-LSTM(R-LSTM) and transfer entropy-LSTM(TE-LSTM). Performance of these models is evaluated by four indicators. The contribution of the main control variables to the transfer temperature is determined based on the mean impact value method. The results show that the accuracy of the models reaches >95 %, which is better than the classical machine learning models. The computational efficiency is improved by 8.93 %∼13.66 %, indicating that the proposed models are reliable. In the future, the method in this study can also be used for determining the tendency of other sensor variables.

Study on the Accuracy of Fracture Criteria in Predicting Fracture Characteristics of Granite with Different Occurrence Depths

The fracture network of a deep geothermal reservoir forms the place for heat exchange between injected fluid and rock mass with high temperature. The fracture resistance ability of reservoir rocks will affect the formation of fracture-network structure, heat exchange and transmission characteristics, and reservoir mechanical stability. However, there are few reports on the fracture toughness and trajectory prediction of geothermal reservoirs with different depths. In this paper, the modified maximum tangential stress criterion (MMTS) is analyzed. The results show that the experimental data are significantly different from the theoretical estimate of MMTS under the influence of different occurrence depths. It is found that the fracture process zone (FPZ) seriously affects the accuracy of predicting fracture initiation angle and mixed-mode (I+II) fracture toughness by MMTS. The FPZ value, considering the influence of different occurrence depths, is modified, and the accuracy of MMTS in predicting the fracture mechanical characteristics of granite is improved. In addition, the mechanical test results show that the Brazilian splitting strength (σt) of granite fluctuates increase with the increase in temperature. With the increase in deviatoric stress, the Brazilian splitting strength and the Brazilian splitting modulus of rock show a trend of first increasing, then decreasing, and then increasing.