Kind Of Reservoir Research Articles

Influence of Heterogeneous Reservoir on Carbon Sequestration and Carbon Displacement

Abstract Carbon Capture, Utilization and Sequestration (CCUS) is a method of burying CO2 captured in various ways into the reservoir and extracting the remaining oil from the reservoir. It is one of the important methods to reduce carbon emissions and achieve carbon neutrality in the next few decades, and it is also considered to be the most economical and effective method to slow down the greenhouse effect. It is very important to study the influence of reservoir heterogeneity on CO2 storage and oil recovery in order to make CCUS scheme store more CO2 and recover more remaining oil. Firstly, the numerical simulation model of reservoir is established in this paper. Its injection-production mode is gas injection in vertical wells at the top of the reservoir at a fixed gas injection rate, and oil production in horizontal wells at the bottom of the reservoir at a fixed pressure. Secondly, the distribution of reservoir porosity and permeability is designed, and four reservoir models are established: homogeneous reservoir, heterogeneous reservoir, positive rhythm heterogeneous reservoir and reverse rhythm heterogeneous reservoir. Finally, the effects of four reservoir models on CO2 storage and oil recovery are studied, and the migration law of CO2 is comprehensively analyzed according to the characteristics of reservoir pressure distribution. The reverse rhythm reservoir has the best CO2 storage effect, and the positive rhythm reservoir has the highest oil recovery. That is, when burying is the main method, the reverse rhythm heterogeneous reservoir is preferred; When oil displacement is the main method, positive rhythm reservoir is preferred. Among the four homogeneous or heterogeneous reservoirs, the migration law of CO2 in reservoirs is quite different, mainly due to the influence of reservoir heterogeneity. CO2 preferentially migrates from the dominant channels in the reservoir, but regardless of the reservoir type, the molar fraction of CO2 at the top of the reservoir is the highest. In addition, the CO2 invasion of four kinds of reservoirs in different stages of caprock is analyzed and its safety is analyzed. This study provides an effective reference for the establishment of numerical simulation models of different types of heterogeneous reservoirs, the migration characteristics of carbon dioxide in reservoirs and the effective operation and evaluation of CCUS scheme.

Schrödinger cats coupled with cavities losses: the effect of finite and structured reservoirs

We discuss the generation of a Schrödinger cat in a nanocavity created by the coupling of an electromagnetic mode with an exciton in a quantum dot considering the dispersive limit of the Jaynes–Cummings model. More than the generation itself, we focus on the effects of the environment over the bosonic state in the nanocavity, which has losses simulated by coupling with two different kinds of reservoirs. In the first case, the interaction of the system with a finite reservoir shows that fragments of different sizes of the reservoir deliver the same amount of information about the physical system in the dynamics of the birth and death of the Schrödinger cat. The second case considers a structured reservoir, whose spectral density varies significantly with frequency. This situation becomes relevant in solid-state devices where quantum channels are embedded, as memory effects generally cannot be neglected. Under these circumstances, it is observed that the dynamics can differ substantially from the Markovian, presenting oscillations related to the average number of photons. These oscillations influence the information flow between the system and the environment, evidenced here by the measurement of non-Markovianity.

Stability of THAI in situ combustion process in reservoirs with layers of grading permeabilities and porosities: Detailed qualitative investigations

The world-wide reserves of heavy oil, tar sand, and bitumen, etc., outweigh those of conventional oil by a factor of 7/3. Given that the conventional reserves are being rapidly depleted, the need to develop and produce the unconventional resources has never been so critical. However, the proven most efficient and environmentally-friendly technology, namely the THAI process, still requires further study, and it has no documented design procedures that factor in the non-ideal geological features of heavy oil and bitumen reservoirs. Throughout the literature, there is little reported on the effects of gradations in reservoir petro-physical parameters on the performance of the THAI process. Consequently, this work reports the results of numerical simulations for four different kinds of reservoirs, each having progressive gradations in permeabilities and porosities. The major findings from this in depth study include.(i) In terms of the temperature distribution, regardless of the permeability and porosity gradations, the high temperature zone is always skewed towards the highest permeabilities and porosities zone. Furthermore, it is found that, in any model in which the shoes of the VI wells have no direct communication pathway with the highest permeabilities and porosities zones of the reservoirs, the high temperature zones occur in two chambers, otherwise, there is one high temperature zone.(ii) It is found that generally, the combustion front tends to be lopsided in favour of the most permeable and porous zone. In the case of a bottom-up progressive increase in permeabilities and porosities (model L1), the single combustion front has greatest advance horizontally at the top and axially in the middle of the reservoir, while in model L2 (the converse of model L1), the combustion fronts propagated in two chambers before the chambers overlapped in the toe region of the HP well where it advanced fastest. Therefore, the combustion zone in model L1 was far more stable than in model L2.(iii) It is found that the combustion fronts in model L3, with the lowest permeabilities and porosities at the centre in the longitudinal direction, propagated in two chambers that overlapped each other around the toe region of the HP well and advanced greatest in the HP well and on either lateral edge of the reservoir. In model L4, which has lateral gradation in permeabilities and porosities, however, the thinner edge of the wedge-shape combustion front had advanced fastest along the vertical mid-plane where the HP well was located. Thus, the combustion zone in model L3 was far more stable than that in model L4.(iv) It is found that in all the models except model L4, there exist rich oil saturation zones in the most permeable and porous regions located ahead of the mobile oil zone (MOZ) of each reservoir. These are formed due to restrictions in the pathways via which the mobilised oil can drain into the HP well. In model L4, the HP well is already in the most permeable zone and consequently, the fluids that favourably reach there are rapidly gravity-drained into the HP well.

A Kist o’ Whistles

A Kist o’ Whistles

Fluid evolution and paleo-pressure recovery by Raman quantitative analysis in the Shahejie Formation of the western slope belt in Dongpu Sag, Bohai Bay Basin, China

Inorganic and organic fluids are widely found in sedimentary basins during oil and gas migration and accumulation. This research investigates two types of sandstone reservoirs with different pressure states and fluid evolution of the Shahejie Formation in the western slope belt of Dongpu Sag. Based on petrographic observations, micro-Raman spectroscopy, and fluorescent spectrometry, petroleum inclusions, CH4-bearing inclusions, and CO2-bearing inclusions were discovered in quartz-hosted minerals. The pressure–temperature–time–composition (P–T–t–X) properties of the CH4 and CO2 inclusions were obtained by quantitative Raman analysis and thermodynamic models. Minimum trapped pressure was predicted by the thermodynamic modeling of petroleum inclusions. Saffron yellow petroleum inclusions represent an early Oligocene oil-charging event (∼32–30 Ma), and the two kinds of reservoirs were all kept in moderate-overpressure conditions (average pressure coefficient: 1.26). Due to rapid uplift and denudation (Dongying movement) in the middle Oligocene in step II, crude oil degrades into CH4 and CO2 (density of CH4 gas inclusions: 0.1010–0.1339 g/cm3; density of CO2 gas inclusions: 0.450–0.612 g/cm3) and retains low-maturity (0.67–1.04%) bitumen in situ. Tectonic destruction causes the reservoir to be released to normal pressure. With the reburial of the Es3 Formation, step II entered the middle stage of oil generation again (average pressure coefficient: 0.90). However, in step I, with secondary hydrocarbons occurring, second-stage oil (performance for pale blue fluorescence in petroleum inclusions) accumulated at ∼12–0 Ma (late Miocene–Pliocene). The second oil charging event in step I remains a reservoir under high-overpressure conditions (average pressure coefficient: 1.67).

Lithofacies and Diagenetic Controls on Tight Silty and Sandy Upper Triassic Reservoirs of the Heshui Oil Field (Ordos Basin, North China)

Summary Tight oil, present in reservoirs of low porosity and permeability, can be regarded as a kind of unconventional resource. The tightening process in this kind of reservoir is controlled by the lithology and diagenetic history of the host formation. Upper Triassic Yanchang Formation siltstones and sandstones are the main reservoirs for hydrocarbon accumulation in the Heshui Oil Field (HOF), southwestern Ordos Basin. The reservoirs exhibit low porosity, low permeability, and strong heterogeneity. In recent years, numerous drillcores have been recovered from these units, but the porosity-permeability characteristics and burial history of these silty and sandy reservoirs have not yet been reported in detail. In this study, an integrated analysis of the lithofacies, diagenesis, and reservoir characteristics of the siltstones and sandstones was achieved using a combination of core and thin section, grain size, scanning electron microscopy (SEM), X-ray diffraction (XRD), δ13C and δ18O, mercury intrusion capillary pressure (MICP), and porosity and permeability data. Our primary goals were to quantify the porosity-permeability characteristics of these silty and sandy reservoirs, restore their diagenetic histories, and examine the paragenetic relationship of reservoir tightness to hydrocarbon accumulation. The silty and sandy reservoirs represent braided river delta facies consisting of compositionally and texturally immature sediments. In the burial environment, they underwent complex diagenetic processes that reduced porosity from an initial average of ~38% to the present ~8%. Porosity-destructive processes included compaction (~ –12.5%) and cementation (~ –21%), with increases in porosity related to grain dissolution (~ +2.2%) and tectonic fractures (~ +1.1%). The reservoirs underwent four diagenetic stages: (1) Penesyngenetic and Eogenetic A Stage (Late Triassic-Early Jurassic); (2) Eogenetic B Stage (Late Jurassic); (3) Early Mesogenetic A Stage (Early Cretaceous); and (4) Late Mesogenetic A Stage (Late Cretaceous to recent). Hydrocarbon charging of these reservoirs occurred in three pulses. Existing pore space was partly filled by hydrocarbons during the Eogenetic B Stage. A second hydrocarbon charging event occurred during the Early Mesogenetic A Stage, when residual primary intergranular pores and secondary dissolution pores were filled. A third hydrocarbon charging event occurred during the Late Mesogenetic A Stage, when the reservoirs were tight. Siltstone beds deposited in delta front environments are the main future exploration targets in the Chang 6 to 8 members. The results of this study provide a useful reference framework for future exploration of hydrocarbon resources in the Upper Triassic Yanchang Formation of the HOF, as well as potential insights into the evolution of similarly tight reservoirs in other basins.

Numerical Simulation of Two-Phase Flow in Glutenite Reservoirs for Optimized Deployment in Horizontal Wells

It is known that the pore media characteristics of glutenite reservoirs are different from those of conventional sandstone reservoirs. Low reservoir permeability and naturally developed microfractures make water injection in this kind of reservoir very difficult. In this study, new exploitation methods are explored. Using a real glutenite reservoir as a basis, a three-dimensional fine geological model is elaborated. Then, combining the model with reservoir performance information, and through a historical fitting analysis, the saturation abundance distribution of remaining oil in the reservoir is determined. It is shown that, using this information, predictions can be made about whether the considered reservoir is suitable for horizontal well fracturing or not. The direction, well length, well spacing and productivity of horizontal well are also obtained.

Required Capabilities for Assessing Depleted and Deep Saline Reservoirs for Successful CCS Projects

Summary Depleted and saline reservoir types are the main candidates to consider for any CCS-scenario. Both kinds of reservoir have fundamentally different risk profiles and degrees of uncertainty and each of them has a role to play in successful CO2 sequestration scenarios. Depleted reservoirs provide a relatively rapid path to storage with significantly less uncertainty on containment and injectivity efficiency. However, the large number of well penetrations that reduce the performance uncertainty also increase the risk of potential leakage points. In contrast, deep saline reservoirs will take longer to bring to project maturity but have by an order of magnitude more storage potential. Additionally, they will almost certainly support super-critical injection in dense phase making the project design much simpler to manage and monitor. Successful long-term CO2 storage projects are likely to employ a combination of both types of reservoirs through a phased life-cycle where the use of a depleted reservoir enables early injection whilst an adjacent saline reservoir is brought ‘on stream’ later on. The implementation of successful CO2 storage projects requires capabilities with strong adjacency to the oil and gas sector, supplemented with those specific to CO2 storage, requiring flexible and adaptable approaches to the upskilling of key staff.

Creating the Conditions for Intergenerational Justice: Social Capital and Compliance

Creating the Conditions for Intergenerational Justice: Social Capital and Compliance

“Second quantitative characterization” and its application in fractured-vuggy carbonate reservoirs

The Ordovician fracture-vug carbonate reservoirs of Tarim Basin, are featured by developed vugs, caves and fractures. The strong heterogeneity results in huge uncertainty when these reservoirs are quantitatively characterized using merely static seismic data. The effective quantitative characterization of the reservoirs has been an urgent problem to be solved. This study creatively proposes the “second quantitative characterization” technique with the combination of dynamic and static data based on the primary static quantitative characterization and fully considering lots of key influence factors when conducting characterization. In this technique, dynamic analysis methods such as well testing, production rate transient analysis, dynamic reserve evaluation and dynamic connectivity evaluation are used to get understandings on this kind of reservoir. These understandings are used as statistical parameters to constrain the inversion of seismic wave impedance to improve the relationship between wave impedance and porosity and determine the fracture-vug morphology, calculate dynamic reserves, and then a more accurate fracture-vugmodel can be selected and used to calculate the oil-water contact inversely based on the results of “second quantitative characterization”. This method can lower the uncertainties in the primary quantitative characterization of fracture-vug reservoirs, enhance the accuracy of characterization results significantly, and has achieved good application results in the fracture-vug carbonate reservoirs of Tarim Basin.

Microscopic Seepage Mechanism of Gas and Water in Ultra-Deep Fractured Sandstone Gas Reservoirs of Low Porosity: A Case Study of Keshen Gas Field in Kuqa Depression of Tarim Basin, China

To study the microscopic seepage mechanism of gas and water in fractured sandstone gas reservoirs of low porosity, this kind of reservoir in the Keshen gas field, Kuqa depression of Tarim basin in China, was taken as an example. Based on rock samples and microscopic visualization technology, nuclear magnetic resonance experiments of saturated water–gas drive and CT scanning experiments of saturated gas–water drive were conducted. The seepage mechanism of water invasion during the gas development were simulated. Subsequently, the distribution of irreducible water saturation and the influence factors on the efficiency of drive were analyzed. The results show that the distribution of gas and water is mainly related to structures of matrix pores, fracture development pattern, and density. The main factors resulting into good reservoirs include large matrix pores and high angle fractures, low irreducible water saturation, and high separation between gas and water. The efficiency of water drive is positively correlated with fracture porosity and dip angle. High angle fractures can effectively improve the seepage capability and then increase the efficiency of water drive. Besides, the great proportion of large pore size in matrix, high fracture dip, porosity, and density can also improve the efficiency of water drive. Therefore, for the development of fractured sandstone gas reservoirs of low porosity, the study of matrix pores and fractures is quite important since it can provide guidance for the efficient deployment of wells. The increase of fracture density is significant by large-scale sand fracturing in order to improve the efficiency of water drive. It is necessary to strictly control the gas production rate of the gas reservoir and delay the water invasion rate as far as possible. In case of serious waterlogging, shut-in all wells in gas reservoirs is a choice to strengthen the gas–water imbibition between fractures and matrix, which can improve the recovery of the gas reservoir.

A proxy model to predict reservoir dynamic pressure profile of fracture network based on deep convolutional generative adversarial networks (DCGAN)

Tight oil and gas reservoirs with huge development potential are widely distributed all over the world and horizontal well technique is a popular development technology for such kinds of reservoirs. However, the efficiency of conventional horizontal well technology is usually unsatisfying due to the unfavorable flow conditions caused by the nature of tight reservoirs, such as low matrix permeability and narrow pore throat. Multi-stage fractured horizontal well technology is an emerging attractive technology that can greatly improve oil production by generating highly conductive fracture networks in tight reservoirs. and numerical simulation method is generally used to predict the production dynamics of the multi-stage fractured horizontal wells. Nevertheless, the complex geological conditions of reservoirs would greatly increase the difficulties and time required to implement a complete simulation (including model building and calculation). Therefore, in this paper, deep convolution generative adversarial networks (DCGAN) based on U-Net framework was applied to establish the dynamic mapping relationship between fracture pattern and reservoir pressure during the production process, that is, the dynamic reservoir pressure distribution can be obtained by image mapping the fracture distribution details. The results showed that the efficiency of U-Net framework based deep convolution in extracting, dividing and splicing the geometric features of fracture network is significant, and the generative adversarial networks model can effectively predict the reservoir pressure distribution according to the fracture network geometry after being trained with 6000 sets of data. Herein, the training accuracy of the proxy model towards sample data was compared, and the confrontation between the generator and the discriminator in the iterative training process was clarified according to the error function. Furthermore, the prediction accuracy towards pressure distribution at different fracture network geometry scales by the proxy model was compared. Results indicated that the pressure diffusion range predicted by the proxy model is basically consistent with the range obtained from the numerical simulation, with a mean square error (MSE) generally smaller than 0.2. In addition, the relationship between the prediction accuracy of the proxy model and the number of sample data and iterative training times was also studied, which showed that the mean square error of the proxy model kept decreasing with the increasing iteration cycles and sample size, which met the basic law of statistical learning. Moreover, it is worth mentioning that the proposed method may also shed light on the applications of DCGAN in other reservoir-related problems.

Injection-production optimization of fault-karst reservoir\u2014considering high-speed non-Darcy effect

Fault-karst reservoirs are featured by complex geological characteristics, and accurate and fast simulation of such kind of reservoirs using traditional simulator and simulation methods is pretty hard. Herein, we tried to discrete the complex fault-karst structures into one-dimensional connected units connecting the well, fracture and cave based on reservoir static physical parameters and injection-production dynamics. Two characteristic parameters, conductivity and connected volume, are proposed to characterize the inter-well connectivity and material basis. Meanwhile, the high-speed non-Darcy seepage term is introduced into the material balance equations for well-fracture-cave connected units to describe the actual seepage characteristics within the fault-karst reservoirs, and to better simulate the oil/water production dynamics. Based on this method, a fracture reservoir model of 1 injection-3 production was established. The change of oil–water action law in different injection and extraction systems under two production regimes of fixed production rate and fixed pressure is analyzed. A case study was conducted on S fault zone, where the flow of oil and gas did not follow the Darcy seepage rule and with a β value of 103–104, the single well flow pressure and oil production were perfectly matched with the real data. In addition, connected units with more prominent high-speed non-Darcy features were found to have better connectivity, which might shed light on the more accurate prediction of inter-well connectivity. Moreover, an improved injection-production well pattern and was proposed based on connectivity prediction model and reservoir engineering method to solve the problems of insufficient natural energy supply and overhigh oil production rate in Block S. Furthermore, the injection/production rate as well as the timing and cycle of water injection was predicted and optimized so as to better guide to site operations.

Inner architectural characteristics of wave-dominated shoreface deposits and their geological implications: A case study of Devonian ‘Donghe sandstones’ in Tarim Basin, China

Wave-dominated shoreface sands are important marine clastic reservoirs, the inner spatial superposition of which causes the complex oil-water relationship in this kind of reservoir, restricting further exploitation; they develops widely in Devonian ‘Donghe sandstones’ of the Tarim Basin in China. Controlled by the genetic mode, static drilling and dynamic development data were applied to analyze these sands—focusing on three orders of architectural units namely the composite sand-bodies (5th order), single sand-body (4th order), and internal component units (3rd order). Furthermore, the identification marks and spatial distribution features of inner architectural units were investigated, and the corresponding architectural model established. Based on methods such as model fitting and control, interface identification, and analysis of well data, the single sand-body and its internal component units were identified, and the spatial superposition relationship was analyzed. In retrograding composite sand-bodies, three types of distribution patterns for the single sand-body including thick-layer refill, step migration, and continuous on-lap are present; contrarily, in prograding composite sand-bodies, the superimposed styles of the single sand-body are primarily thick-layer cumulation, step migration, and continuous overlay. The single sand-body is divided into one or more internal component units by the architectural interface of 3rd order, presenting a low-angle landward or seaward migration style. The oil-water distribution in wave-dominated shoreface reservoirs is substantially influenced by sand architecture, and architectural interfaces of different orders separate the sedimentary sand-bodies into relatively independent fluid systems, leading to differences in oil-gas production possibility among the independent layers. The wave-dominated shoreface architectural model can provide reasonable explanations for contentious factors such as the oblique oil-water interface, and production contradictions such as the mismatch between water injection and oil recovery, and resolve disagreements on well-deployment through prediction of the distribution of remaining oil, all of which have great significance for oil and gas exploration and production.

Study on Water Injection Indicator Curve Model in Fractured Vuggy Carbonate Reservoir

Fractures and cavities are very well developed in fractured vuggy carbonate reservoirs in Tahe Oilfield, showing obvious constant volume or approximate constant volume characteristics, and the development of karst vuggy reservoirs is characterized by strong randomness, locality, heterogeneity, and discontinuous development, which has a great impact on oilfield development effect. The application of conventional reservoir engineering methods in this kind of reservoir has many limitations. The traditional water injection indication curve is mainly based on a sandstone reservoir, ignoring the elastic energy of the water body in a reservoir and the combination relationship of fracture and cavity, which can not meet the needs of the carbonate reservoir. According to the principle of volume balance of constant volume body and considering the elastic energy of original formation water, a new model of improved water injection indication curve and the original water-oil ratio of carbonate reservoir is proposed, and the chart of water injection indication curve is established. Compared with other methods, this method has the advantages of low cost and accurate identification results. The calculated reservoir parameters such as single well-controlled reserves, well-controlled water volume, and original water-oil ratio have high reliability, and the chart is easy to use. The model is applied to the Yuejin block of Tahe Oilfield, and the results show that the improved model is consistent with the results of other test methods, such as high-precision seismic combined with fracture cavity carving technology, which indicates that the model has strong reliability.

전통적 水利시설의 근대적 변동양상— 漢灘江水系 鐵原･漣川지구의 사례 —

This paper is to clarify the modern reorganization process of traditional irrigation facilities such like Bo(洑) and Zeon(堤堰) in the modern transitory period, Korea rural. Zeon is a kind of reservoir, and Bo is an irrigation canal from the river-bank. In the perspectives of local society history, these traditional facilities in Cheorwon(鐵原) and Yeoncheon(漣川) county, Hantangang-river(漢灘江) valley, had continued long-term existence in the transitory period, colonial period. The case of Bo(洑) shows these characteristics well. This remarkable facts displays long-term sustainability of local irrigation community in a peasant community. Especially, historical materials in Joongang Irrigation Association(中央水利組合) of Cheorwon county present a lots of traditional irrigation facilities in the upstream of the Hantangang-river. This case study brings light on the research of close corporate community in context of East Asian studies.

Comparative Study on the Reservoir Characteristics and Development Technologies of Two Typical Karst Weathering-Crust Carbonate Gas Reservoirs in China

Carbonate reservoirs are the main reservoir types in China, which occupy the large ratio of reserves and production at present. The high-efficiency development of carbonate reservoirs is of great significance to assure the stability of national energy supply. The Lower Paleozoic reservoir in Jingbian gas field and the Sinian reservoir in Anyue gas field are two typical carbonate gas reservoirs, and their successful development experiences can provide significant references for other similar carbonate gas reservoirs. For Jingbian gas field, it is a lithological-stratigraphic reservoir developed in a westward monocline and multiple rows of nose-fold structures, and is a stable craton basin with simple palaeognomy distribution and stable connectivity, which has complex gas-water distribution. However, for Anyue gas field, it is a lithological-structural reservoir with multiple tectonic high points and multiple fault systems, and is biological dune beach facies under extensional setting with highly differentiated inside of the block in palaeognomy characteristics, which has limited connectivity and tectonic side water is in a local area. The difference of gas reservoir characteristics leads to the diverse development strategies. For these two gas reservoirs, although there are some similar aspects, such as the screen of enrichment areas, the application of irregular well pattern and reservoir stimulation techniques, the criteria of enrichment areas, the well types, and the means of reservoir stimulation are absolutely different. In addition, due to the differences of control reserves and production capacity for these two kinds of reservoirs, the mode of stable production is also different. The effective development of Jingbian gas field can give some references to the future exploitation on the Sinian gas reservoir. Firstly, the sedimentary characteristics should be studied comprehensively. Secondly, the distribution pattern and distribution characteristics of the palaeognomy should be found and determined. Thirdly, the distribution of fracture system in the reservoir should be depicted finely. Finally, dynamic monitoring on the production performance should be strengthened, and the management for this gas field should be improved further. The findings of this study can help for better understanding of the Karst weathering-crust carbonate gas reservoir formation characteristics and the optimal development technologies that should be taken in practice.

Evaluation method for low- to ultralow-permeability reservoirs based on pore-throat structure: A case study in the eastern Nanpu Sag, Bohai Bay Basin, China

The pore-throat structure of low- to ultralow-permeability reservoirs is complex, causing the permeability to vary greatly under similar porosity conditions. Moreover, the pore-throat structures are the key factors that controled the physical properties of such kind of reservoirs. Therefore, conventional reservoir evaluation methods can hardly meet the research needs of low- to ultralow-permeability reservoir exploration and development. We have conducted our research on Paleogene Shahejie and Neogene Dongying low- to ultralow-permeability reservoirs in the eastern Nanpu Sag of the Bohai Bay Basin to address this issue. Cores, thin sections, and scanning electron microscopy were used to analyze the pore-throat structures to determine the characteristics of low- to ultralow-permeability reservoirs, and a new parameter for evaluating low- to ultralow-permeability reservoirs is developed. The results of this research show that primary pores, secondary pores, and microfractures are developed in the study area and that the pore-throat shape is mainly flaky or curved flaky. The microscopic pore-throat structure controlled the reservoir physical properties and fluid mobility of these reservoirs, the permeabilities of these reservoirs are dependent on the pore throats, and the correlation between connected pores and permeability is strong. Based on the analysis of the pore-throat structure, as well as the maximum mercury saturation (Smax) and the residual mercury saturation (Sr) at the maximum pressure and the minimum pressure obtained by the mercury injection test, an evaluation of the reservoir by using the mobility parameter of fluid (Δfm = Smax-Sr) is proposed, and the pore-throat radius R15 obtained by the mercury intrusion experiment has the best correlation with the fluid mobility parameters. The mobility parameters of fluid can effectively improve the accuracy of logging interpretation of low- to ultralow-permeability reservoirs and provide a scientific basis for the scale stimulation and effective development of low- to ultralow-permeability reservoirs.

A well selection method of CO2 huff and puff in heavy oil reservoir with edge and bottom water based on water cut

The water cut of heavy oil reservoir with edge and bottom water rises rapidly and the recovery degree of crude oil is low. CO2 huff and puff is an effective measure to improve the recovery of this kind of reservoir, and scientific well selection is the premise of the measure effect. Because the existing well selection methods of CO2 huff and puff in heavy oil reservoir with edge and bottom water mostly take the oil increase of oil well as the evaluation index, ignoring the characterization of well water cut after huff and puff, it is unable to accurately screen all potential wells. Therefore, a quantitative well selection method of CO2 huff and puff in heavy oil reservoir with edge and bottom water based on water cut is proposed. The method is based on fuzzy comprehensive evaluation theory and analytic hierarchy process, and takes the water cut after CO2 huff and puff as the evaluation index. Several groups of typical models are designed to screen the sensitive factors and laws of CO2 huff and puff well selection in heavy oil edge and bottom water reservoir from three aspects of geology, water production law and technology. Than the judgment matrix is established. There is little interference from human factors in the process of well selection, and the rationality of the method has been verified by the effect of field actual well measures. This method is helpful to improve the well selection method system of CO2 huff and puff in this kind of reservoir, and is a reasonable supplement to the existing well selection method which takes the oil increment as the only evaluation index.

Mechanism research on technical policy of liquid extraction depressurization development for buried hill reservoirs

Most of buried hill reservoirs are in the late stage of water flooding development, especially for this kind of reservoir with large water-oil volume ratio, it is more difficult to develop the residual oil in matrix system. This article presents a new idea about technical policy of extraction depressurization development which has not been studied in domestic and abroad, and analyses the major influence factor of liquid extraction depressurization by dual-media numerical simulation in depth. The results show that it can increase the oil production in matrix system to a greater extent by liquid extraction depressurization. The liquid extraction capacity is the most important factor which contains the effect of uniform speed liquid extraction, variable speed liquid extraction and periodic liquid extraction. Under the condition of keeping stable production, the larger the liquid volume extracted, the faster pressure dropped, and the more oil will be discharged in matrix system. According to these results, this paper suggests the reasonable technical policy of liquid extraction depressurization, and it is of great significance to obtain good effect of slowing down water cut and enhancing oil recovery in depressurization development of the buried hill reservoirs with high water cut and enough energy.