Oil-bearing Area Research Articles

Main spatial-temporal regularities of the state of the chemical composition of groundwater of the oligocene aquifer in the Shaim oil and gas bearing area

The constantly growing need for fresh water in the Shaim oil and gas region necessitates the exploration of new areas and the development of measures to improve the operation of water intakes. To predict the quality of groundwater, which is an operational parameter of the aquifer aquifer, it is needed up-to-date information on the chemical composition of ground-water. The aim of this study to identify main spatial-temporal regularities of the state of the chemical composition of groundwater of the oligocene aquifer in the Shaim oil and gas bearing area, compared to average values from adjacent areas. Research methods include the systematization of laboratory data on water samples, analysis of groundwater chemistry, and mapping of the main spatial-temporal patterns in component concentration changes. The average values of chemical composition indicators in the studied area are similar to those of neighbouring areas, with some indicators exceeding drinking water standards. Similarities are observed in the variability of the chemical composition, spatial patterns of changes in most chemical indicators, and the presence of areas with extreme values. Current data on the chemical composition of the oligocene aquifer ground-water, including key characteristics and spatial-temporal trends presented in distribution maps, can be used in designing groundwater intakes and forecasting long-term groundwater quality.

Research on fault lateral sealing of thinly interbedded sandstone and mudstone strata based on the fine calculation method of the SGR value

Terrestrial sedimentary basins are influenced by rapid changes in the clay content, resulting in significant differences in the lateral sealing capacity (shale gouge ratio, SGR) of different parts of the fault. In the present study, we used a method of setting virtual wells and using seismic inversion data to accurately calculate the SGR of faults in strata composed of interbedded sandstone and mudstone calculate the clay content of the strata and to compensate for the low level of the actual well control. Optimal well spacing was determined based on the variable clay content of the formation. The planar variation of the fault throw was characterized via seismic interpretation. We also examined the lateral sealing of faults. The Putaohua oil layer in the S14 area of the Sanzhao Sag in the Songliao Basin was chosen as an case study. Based on the calculation of fault SGR values and the oil distribution, the evaluation criteria for the fault sealing capacity were determined, and the changes in the lateral sealing capacity of the faults were analyzed. This approach accurately estimates fault SGR values and predicts the effective oil-bearing area within the fault zone. It is also suitable for evaluating the lateral sealing of faults in strata composed of interbedded sandstone and mudstone. Our findings provide an in-depth understanding of the lateral sealing of faults and can aid in further research on petroleum distribution patterns.

Pore-Scale Oil-Water Flow Behaviors in Different Development Adjustment Schemes for Enhancing Oil Recovery in Waterflooding

Development mode adjustment is an important measure to further enhance oil recovery after primary waterflooding. Investigating the oil-water flow behaviors in the pores is significant to deepening the understanding of the macrobehavior of waterflooding and the designation of the reservoir development plan. Previous studies mainly focused on the change in recovery factor and macroflow characteristics, while less attention was paid to the causes of the change in recovery factor and the difference in macrocharacteristics. In this paper, the numerical simulation technology by coupling the Navier-Stokes equation with the method of volume of fluid is employed to investigate the dynamic formation mechanism of the remaining oil at pore-scale in the primary waterflooding, and then the pore-scale oil-water two-phase behaviors under three waterflooding development adjustment schemes: changing flooding direction, turning extraction well to injection well, and increasing injection rate are studied. The research shows that when the viscous resistance of the water-bearing channel is less than the sum of the capillary barrier and drainage capillary resistance (the resistance in the displacement of wetting phase displacement using the nonwetting phase), the remaining oil is formed. Water➔oil➔water➔oil displacement mode is formed in the process of changing flow direction, which makes the force of the phase interface tend to balance, reduces the capillary effect in waterflooding, and improves oil recovery. In the process of developing the scheme of turning extraction into an injection well, through multipoint injection, it advances from the central water-bearing area to the oil-bearing area on both sides in multiple paths, forming a larger spatial spread range than that in the change of flooding direction. Under the influence of the capillary barrier effect and drainage capillary resistance, when the injection rate is increased, the remaining oil can restart to move only when the flowing rate exceeds a certain value. The small viscous resistance in the water-bearing channel and the lateral resistance from the capillary barrier limiting the lateral sweep of water are the primary reasons for the insignificant improvement of oil recovery under the condition of a low liquid injection rate. The findings of this study can help for better understanding of pore-scale flow mechanism behaviors and their influences on the macroscopic development features in the waterflooding process.

Geological model and prospects of oil and gas bearing deposits of the silurian complex of the Pechora sea shelf

The task of this work is the desire of the authors to draw attention to the problem of ac-celerating the pace of searches for promising Arctic objects on the shelf of the Pechora Sea and additional exploration of already discovered deposits in the Silurian oil and gas complex on the territory of the Varandei-Adzva structural zone (VASZ). The main result of the previously per-formed offshore exploration work is the identification of a new oil-bearing area in the eastern part of the Pechoromorsky shelf. Large oil fields have been discovered here: Prirazlomnoye, Varandey-sea, Medynskoye-sea, Dolginskoye. The proven reserves and resources of hydrocarbons (HC) allow us to assume that in the near future a new oil-producing area will be formed on the shelf of the Pechora Sea. In total, the initial raw oil resources in the Pechora Sea are more than 3500 mln tons. Keywords: Pechora sea; silurian oil and gas complex; silurian; oil.

Channel Evolution under the Control of Base-Level Cycle Change and the Influence on the Sustainable Development of the Remaining Oil—A Case in Jiang Ling Depression, Jiang Han Basin, China

The extension of river channels is one of the key factors in determining the remaining oil distribution. Different sedimentary facies and bedding types of oil layers will form specific characteristics of remaining oil distribution after water injection development. Using massive drilling, core, logging, seismic, and production data, on the basis of sequence stratigraphy base-level cycle change, the river records and development history are restored, and the fine connectivity of reservoirs and the configuration relationship of production wells are studied. The following conclusions are drawn: (1) A sequence stratigraphic division scheme is established. In the established sequence framework, the types and characteristics of reservoir sand bodies are analyzed. The 2nd and 6th members of Yu yang formation can be divided into 2 long-term base level cycles, 5 medium-term base level cycles, and 17 short-term base level cycles. The evolution of the second and sixth members of the Yu yang formation shows a pattern of base level rising, falling and rising again; (2) the vertical sedimentary evolution sequence is underwater distributary channel distributary channel meandering channel distributary channel flood plain. The types of channel sand bodies developed from little overlap to more vertical or lateral overlap and then gradually changed to isolated type; (3) according to the structural location and development sequence, different types of reservoirs are identified. Combined with the statistics of the drilled data of Yu yang formation k2y4 in Fu I fault block, it is found that the connectivity rate of oil layer thickness (the ratio of oil layer connectivity thickness to total thickness of sand layer) within the oil-bearing area is 84.4%, and the connectivity rate of the number of layers (8) is 60%. The connectivity condition is relatively good.

Study on Screening Criteria of Gel-Assisted Polymer and Surfactant Binary Combination Flooding after Water Flooding in Strong Edge Water Reservoirs: A Case of Jidong Oilfield.

Strong edge water reservoirs have sufficient natural energy. After long-term natural water flooding development, it is in the stage of ultrahigh water cut. There is an urgent need to change the development mode and improve the development effect. Taking Jidong Oilfield as an example, the mechanism model of strong edge water reservoirs is established by using the method of numerical simulation. Then, the factors and rules affecting the effects of gel-assisted polymer and surfactant binary combination flooding are studied. The screening criteria of gel-assisted polymer and surfactant binary combination flooding in strong edge water reservoirs are obtained. The results show that the existence of edge water is not conducive to binary combination flooding. Smaller water volumetric multiples and larger oil-bearing areas are more suitable for binary combination flooding. Compared with closed reservoirs, binary combination flooding in strong edge water reservoirs is more difficult to establish a displacement pressure gradient. The reservoir with high crude oil viscosity is not suitable for binary combination flooding. Gel-assisted polymer and surfactant binary combination flooding can be adopted for reservoirs with an oil-bearing area greater than 0.2 km2, a water volumetric multiple less than 200, and oil viscosity less than 100 mPa·s. The research results are of guiding significance for the reservoir selection of gel-assisted polymer and surfactant binary combination flooding after natural water flooding.

Normal fault transmissibility characteristics under the transition condition of fault conduction and sealing observed in simulation experiments

In rift basins, normal faults conducting and sealing fluids are the main mechanisms for evaluating fault-related reservoirs, and the defined threshold value of fault conduction or sealing is based on statistics. However, fault transmissibility characteristics under a transition condition of fault conduction and sealing have not been clarified. This study used structural deformation and hydrocarbon charging as a foundation to quantitatively characterize fault transmissibility under the transition condition of fault conduction and sealing. This study examined faults occurring in sandstone–mudstone interbeds and used the fault throw and mudstone content as the main variables. The physical simulation results revealed that despite all models exhibiting simple “one-layer” fault architecture with only a fault core, their internal composition undergoes a sequential change from the mudstone drag, mudstone drag and sliding surface to the mudstone breccia and sliding surface. Similarly, when the fault is in the transition condition of fault conduction and sealing under the constraints of mudstone, a normal distribution is observed in terms of the number of oil-bearing layers, oil-bearing length, and oil-bearing area of the lateral fault conduction. However, when the shale smear factor (SSF) is too high, the “one-layer” fault architecture mainly comprises the mudstone breccia and sliding surface, which increases the vertical fault transmission and reduces the lateral fault conduction. Conversely, an excessively small SSF, where the fault zone is a “one-layer” fault architecture comprising mainly the mudstone drag or mudstone drag and sliding surface, will restrict the vertical fault transmission and reduce the lateral fault conduction. When the lateral fault conduction near the inflection point of the normal distribution reaches its threshold, the superposition of mudstone along the fault and the presence of mudstone breccia in the fault zone become critical for decelerating the vertical fault transmission and accelerating the lateral fault conduction. The study of normal fault transmissibility characteristics under the transition condition of fault conduction and sealing provides a solid theoretical foundation for the risk assessment of fault-related hydrocarbon accumulation.

Experimental Study on Microscale Simulation of Oil Accumulation in Sandstone Reservoir

It is generally believed that conventional hydrocarbon accumulates in sandstone traps after migrating at a certain distance. Unconventional hydrocarbon only migrates at a short distance before accumulation or being imbibed in the tiny pores of shale and tight sandstone reservoir, and there is no obvious trap boundary. There are also different views on the time interval between hydrocarbon accumulation and migration. In this paper, microscale simulation experiments are used to study the process of oil accumulation during migration. In the single pore-throat model, oil can 100% saturate the pore in the process of migration with continuous oil supply. In the plane sandstone model, when oil migrates through the entire model, the oil-bearing area can reach more than 50% of the model area. In the sandstone reservoir model, when the front edge of oil migrates through the entire sandstone layer, the oil saturation near the injection point can reach more than 90%, while the oil saturation of the front part of the model is only about 50%. It shows that, in sandstone reservoir, when there are sufficient oil source and continuous charging pressure, the oil saturation near the charging point continues to increase during oil migration, and the range of high oil-bearing area continues to expand. Therefore, there can be a certain number of hydrocarbon accumulations along the migration path in sandstone reservoir under sufficient oil supply and continuous charging pressure, rather than just in traps.

Study of the horizontal sidetracking efficiency using hydrodynamic modeling (on the example of a Kazakhstani field)

One of the modern approaches for the effective development of small deposits is the construction and operation of wells with a complex architecture: horizontal wells (HW), sidetracks (BS, BGS), multilateral wells (MLW). Sidetracking makes it possible to reanimate an old well that is in an emergency state or inactivity for technological reasons, by opening layers that have not been previously developed, bypassing contamination zones, or watering the formation. This study examines the possibility of using horizontal sidetracks in the operating wells of the field of the Zhetybai group. To select the optimal length of the horizontal sidetrack of the wells, graphs of the dependences of the change in flow rate versus length of the horizontal well were built, taking into account the pressure losses due to friction. It can be seen from the dependence of NPV versus length of the horizontal wellbore that the maximum NPV is achieved with a horizontal wellbore length of 100 m. A further increase in the length of the horizontal wellbore leads to a decrease in NPV. This is due, firstly, to a decrease in oil prices, and secondly, interference of wells, a small number of residual reserves, and a small oil-bearing area. As a result of a comparison of technical and economic criteria, the optimal length of a horizontal wellbore is from 100-300 meters. Comparison of the flow rates of vertical wells and wells with horizontal sidetracks showed a clear advantage over the latter in all respects.

On the questions of supply of active gas raw materials in central Yakutia

The article deals with the problem of the reliability of the balance gas reserves of the Vilyui oil and gas region calculated by the volumetric method. Based on the analysis of the development of gas and gas condensate fields of the Predverkhoyansk and Vilyui oil and gas bearing regions, the low production capabilities of the depleted fields of the region are shown. It is concluded that the most reliable in the conditions of a complex geological structure of deposits is the assessment of gas reserves by the pressure drop method. The idea is formulated that for the fields of the Vilyui oil and gas bearing area, which have productive horizons with low initial gas saturation of reservoirs, the final gas recovery factors can be estimated at 0.55. The expediency of considering the issue of the special status of the Srednevilyui gas condensate field as a field with strategic gas reserves is noted.

Study on oil-water interface of Budate fracture reservoir in each block of Suderte Oilfield

It is well known that in addition to bound water in the reservoir, formation water mainly exists in the form of edge water and bottom water. Fractured buried hill metamorphic rock reservoirs are generally bottom-water reservoirs. In fractured reservoirs, rock blocks are cut by fractures and oil and water are distributed in fractures. Due to the low capillary pressure of fractures, the oil-water transition zone is also small. In the same fault block, there is relatively uniform oil-water interface. And oil-water interface to judge correctly or not will directly related to the determination of oil-bearing area and effective thickness division and well placement, thus correctly determine the position of the oil-water interface of oil field development is of great significance, through the variation of oil-water interface also presumably or some guidance on the seismic section can't precisely divide the small fault.

Comprehensive study of the geological structure Verkhneyakovlev deposits of the Tagul field in the process of justifications for operational drilling

Currently, most of the fields being put into development are characterized by a complex geological structure, both in terms of section and in terms of plan. The solution of all geological tasks, including such important ones as the preparation of exploration projects, operation and effective development management, is impossible without creating models that reflect the main features of the variability of target parameters. The construction of adequate models of objects with a complex structure requires the involvement of all available information. The accuracy of the geological model is mostly determined by the accuracy of the well correlation. Paleosols are a new marker for the complex-built layers of the VAk-2 and VAk-3(1) of the Tagul field, which contributes to the validity of the correlation of the section of these layers. The reliability of the model was also improved by the use of the results of facies analysis. This analysis showed that the sedimentation of the studied objects includes channel and floodplain facies. Reservoir rock properties of these facies differ significantly. The updated model is characterized by a reduction in the oil-bearing area and the amount of reserves. The implementation of the model will optimize the project fund of wells and reduce the cost of well intervention. Economically, this means reducing capital costs and increasing the profitability of the project.

Revealing of the effect of borehole deviation on its productivity

The wells drilled with the deviation angle compared to the vertically drilled ones cover more of oil-bearing area. By increasing drainage zone it is possible to obtain high final oil production and therefore, to enhance oil recovery rate. With the purpose of reducing the drilling costs, the increase of drainage zone gives positive outcomes. From economic point of view, it is more efficient to operate the field increasing the well quantity (i.e. well density) or to use horizontal wells drilled with deviation angle.

Synergistic Modes and Enhanced Oil Recovery Mechanism of CO2 Synergistic Huff and Puff

With the gradual declining of oil increment performance of CO2 huff-and-puff wells, the overall oil exchange rate shows a downward tendency. In this regard, CO2 synergistic huff-and-puff technologies have been proposed to maintain the excellent effect and extend the technical life of such wells. However, there is no specific research on the mechanism and synergistic mode of CO2 huff and puff in horizontal wells. This study aims to establish the synergistic mode and determine the adaptability and acting mechanism of CO2 synergistic huff and puff. Three synergistic huff-and-puff modes are proposed based on the peculiarity of the fault-block reservoir’s small oil-bearing area and broken geological structure. We establish three typical CO2 synergistic huff-and-puff models and analyze the influence of different geological and development factors on the huff-and-puff performance with numerical simulation. Each factor’s sensitivity is clarified, and the enhanced oil recovery (EOR) mechanism of CO2 synergistic huff and puff is proposed. The sensitivity evaluation results show that the reservoir rhythm, inter-well passage, well spacing, high-position well liquid production rate, and middle-well liquid production rate are extremely sensitive factors; the stratum dip and injection volume allocation scheme are sensitive factors; and the relationship with structural isobaths is insensitive. The EOR mechanism of synergistic huff and puff includes gravity differentiation, supplementary formation energy, CO2 forming foam flooding, and coupling effect of production rate and oil reservoirs. The implementation conditions of the two-well cooperative stimulation mode are the simplest. The two-well model is suitable for thick oil layers with a positive rhythm and large formation dip. The single-well mode requires no channeling between the wells, and the multi-well mode requires multi-well rows and can control the intermediate well’s fluid production rate. Field application at C2X1 block shows a good performance with a total oil increment of 1280 t and an average water-cut reduction of 57.7%.

OIL AND GAS COMPLEXES OF THE ALDANO-MAY OIL AND GAS REGION

The article discusses the history of the geological study of the Aldan-Maya oil and gas region, during which numerous signs of oil and gas potential were identified. The description of oil and gas bearing complexes of sedimentary strata is given. It is shown that the prospects for the discovery of new oil and gas fields in the Aldan-Maya oil and gas bearing area were assessed quite high.

An innovative method for the characterization of oil content in lacustrine shale-oil systems: A case study from the Middle Permian Lucaogou Formation in the Jimusaer Sag, Junggar Basin

Determination of oil content not only affects the exploration and development of potential favorable intervals in lacustrine shale-oil systems but also impacts research on the main factors controlling the differential accumulation of shale oil. Current approaches usually characterize a certain fraction of the hydrocarbons in shale oil. For example, the volatile hydrocarbon (S1) fraction is considered to represent the hydrocarbons (C7–C33) that would be volatilized below 300 °C. In this article, an innovative method called the oil content evaluation index (OCEI) is proposed, in which the shale oil composition is considered and used to evaluate the vertical distribution of oil content utilizing conventional logging. In the OCEI method, the evaluation index (LI*) represents the content of liquid hydrocarbons per unit mass of rock; this index successfully characterizes the discrete experimental data S1 and chloroform extract yield. The evaluation index (CI*) represents the oil-bearing area under the core description. The evaluation index (GI*) characterizes the content of gaseous hydrocarbons in a constant volume. Based on the relationship between these evaluation indexes and the actual production, the relative weight of each evaluation index is determined through the grey relational analysis method. Finally, the OCEI value is the sum of the product of these normalized evaluation indicators and their corresponding weights. In a case study, the method is successfully implemented to predict the pay zones of the Lucaogou Formation in the Jimsar Sag, Junggar Basin, China. The threshold value of OCEI is set to 0.39 based on its relationship with production data. When the OCEI value of a certain interval is greater than 0.39, then this interval is a favorable pay zone. The evaluation results of two wells in the Jimusaer Sag further demonstrate that the model can effectively and reliably predict potential favorable intervals in shale oil systems.

The technology of effective reservoir prediction in fault development zone

Reservoir prediction in the middle and late stages of development is not only to predict the sandstone, but also to define the specific location of Petroleum-bearing sandstone. The post-stack seismic data is superimposed on a multi-channel seismic data level, although the signal-to-noise ratio is improved to a certain extent, the average amplitude value is obtained in the superposition process, so that only the effective prediction of the sand body can be realized. However, the pre-stack seismic data can obtain the information of shear wave by the longitudinal wave. The characteristics of the shear wave that cannot propagate in the fluid can effectively predict the reservoir and fluid distribution. In order to further quantify the remaining oil potential in fault area, prestack seismic inversion technology and petrophysical analysis are used to determine the favorable oil-bearing area. On this basis, prestack geostatistical inversion is completed to further clarify sand body with high oil saturation. Combined with numerical simulation, it effectively predicts the residual oil distribution at the edge of fault and the precision of the remaining oil quantitative characterization results is high. The recognition rate of thick layer saturation is more than 90%, and the recognition rate of thin interlayer saturation is more than 70%, which can meet the demand of fine reservoir prediction.

Pre-stack Q estimation based on inverse spectral decomposition

The quality factor can quantitatively measure the attenuation of seismic waves, and it can compensate for seismic wave amplitude attenuation and correct the phase distortion. The traditional Q extraction method uses the post-stack seismic data to extract the Q-factor. Due to the low-pass filtering effect of the stacked seismic data, the obtained quality factor may be inaccurate. A method of estimating the quality factor using pre-stack common midpoint (CMP) gather data is proposed in this paper. In this method, inversion spectrum decomposition (ISD) and shaping regularization are introduced to obtain the Q-factor. During the process, we obtained the average-Q through inversion and finally obtained the internal-Q by using the average-Q. The numerical simulation and field data application show that the Q obtained using this method can accurately identify the oil-bearing area. Then, the Q is applied to the inverse Q-filter and produces seismic data with a high resolution and a high signal-to-noise ratio.

Quick assessment to ascertain technical rational well spacing density in artificial water flooding oilfield

Optimization of technical rational well spacing density (TRWSD) is a crucial part of the study of oilfield development. However, the methods widely used previously have some disadvantages as followings: (1) Some quoted theories and formulas for algorithms are intractable. (2) Some are incompatible with the reality as they assumed too many conditions which are more ideal. (3) The influence factors considered by other algorithms are not comprehensive and irrational. (4) In applications, the applicable conditions are ignored by some algorithms. Aiming at the problems above, this paper has built a quick estimation model of TRWSD and proposed a new optimizing method of TRWSD, based on the comprehensive investigation of pressure distribution and the theoretical model of rational ratio of oil to water wells (RROWW) in artificial water flooding oilfield. Verification by reservoir numerical simulation model and actual data of the field implementation shows that the TRWSD model is reliable, and practical. It is revealed from the studies that the injection-production pressure system factors are the main ones to control TRWSD except water cut, such as the oil-bearing area of producing geological reserves, liquid productivity index, injection-production ratio and number of injection-production wells, and so on. And compared with the previous ones, the TRWSD method comprehensively takes into account such the factors as injection-production unbalance, density difference between oil and water, volume factor, start-up pressure gradient of injection wells, start-up pressure gradient of production wells and so on. Hereinafter, the new model can be applied for the calculation of the TRWSD and related parameters at any injection-production development stages, reservoir types and reservoir pressure distributions in artificial water flooding oilfield, all of which means that the new method has a strong promising adaptabilities and prospects in the water flooding oilfield with close well spacings or during high water cut stage.

Prospects and Forecasting of Deep-Seated Oil and Gas Reservoirs of the Meso-Ceno Deposits of Azerbaijan

Recently, in the Republic has been deploying drilling explorations from the eastern part to less studied central and western areas. In this reason, had a particular importance the generalization of the available geological and geophysical materials related to the new focus territory, the evaluation of the prospects of individual lithologic-stratigraphic complexes and the forecasting of deep-seated oil and gas reservoirs. Studies carried out in this direction are given in this paper, which describes the analysis of different petrophysical data. At the same time were re-interpreted reservoir and petrophysical properties of rocks, mesocenozoic deposits taken from the drilled exploratory wells and geological material of the areas of oil and gas bearing area, where are widely distributed deposits of the productive strata (PT-lower Pliocene). As a result of analysis and interpretation of geological, geophysical and petrophysical date, it has been established that oil-and- gas-bearing reservoirs are mainly fractured volcanogenic-sedimentary and carbonate rocks.