Changes In Reservoir Parameters Research Articles

Numerical Simulation of Time-Varying Characteristics in a High-Permeability Sandstone Reservoir: A Case of Gaoqian Southern Area

In the process of long-term water flooding in the Gaoqian Southern Area with an average porosity of 30% and an average permeability of 1333.5×10−3 μm2, the fluid-solid interaction among oil, water, and rock has a great influence on the pore structure. It has resulted in changes in reservoir parameters with the extension of time. This paper used electron microscopy scanning, mercury injection, X-ray diffraction, physical properties, and oil-water relative permeability curves to study the variation of clay mineral content, pore throat structure, porosity, permeability, and relative permeability curves of high-permeability sandstone after high-pressure water flooding. The results showed that clay minerals such as montmorillonite and kaolinite were dissolved, hydrated, and migrated after long-term water flooding, which resulted in the decrease of clay mineral content in fine sandstone and medium sandstone, the increase of pore throat radius, and the decrease of displacement pressure, median pressure, and separation coefficient. The saturation of the isotonic point of the oil-water relative permeability curve was obviously shifted to the right, the hydrophilicity was significantly enhanced, and the porosity and permeability were effectively improved, but there was a blockage of the throat less than 2 μm in the fine sandstone. In addition, this paper established the equations of water injection, permeability, irreducible water saturation, residual oil saturation, and oil-water relative permeability curve coefficient and establishes the initial permeability model with the well data before water flooding. The logging interpretation results of development wells in the process of water flooding as verification data were used, and the relative error of permeability far lower than the general requirement of permeability error within an order of magnitude was less than 30%, which verified the rationality of the method.

STUDY OF THE PERFORMANCE OF THE DYNAMIC LEVEL STABILIZATION SYSTEM OPERATION IN THE WELLBORE EQUIPPED WITH AN ELECTRICAL SUBMERSIBLE PUMP UNIT

Link for citation: Totanov A.S., Molchanova V.A., Urazakov K.R. Study of the performance of the dynamic level stabilization system operation in the wellbore equipped with an electrical submersible pump unit. Bulletin of the Tomsk Polytechnic University. Geo Аssets Engineering, 2023, vol. 334, no. 8, рр. 210-219. In Rus. The relevance of the study is related to the widespread use of electrical submersible pump units in the production of low-viscosity oils and water-gas-oil emulsions at this stage of development of mechanized production. However, the current production conditions associated with changing reservoir parameters bring to the fore a number of technical problems that need to be solved. One of these challenges is the phenomenon in which the dynamic level of the well decreases due to changes in reservoir parameters (reservoir pressure, productivity factor, etc.). Decrease of dynamic liquid level in the well leads to complications during operation of electrical submersible pump units. As a consequence, the increased cavitation in impellers is possible due to pressure reduction on the pump intake, and also full pump supply failure is not excluded at significant reduction of the dynamic level of the borehole fluid. In this relation, a technical solution, consisting in installation of bypass device (electrical valve) above the place of suspension of electrical submersible pump plant to maintain stable dynamic liquid level in the well and avoid complications during pump operation, was suggested. To confirm the feasibility of the dynamic level stabilization system, a mathematical model was developed to evaluate the effectiveness of complication prevention with the help of the proposed technical solution during the operation of the electric centrifugal pump unit. The main aim of the research is to develop a calculation method for studying the dynamics of the dynamic level stabilization system. Objects: an electrical submersible pump unit in conjunction with a system for stabilizing the dynamic level of the well. The influence of the diameter and length of the electrical valve on the efficiency of the dynamic level recovery was studied, taking into account hydraulic losses during the system operation. Methods. The research method is reduced to numerical solution of differential, linear and non-linear equations describing flow and pressure at electrical submersible pump unit outlet in steady-state mode, fluid flow through the electrical valve taking into account hydraulic resistances, flow of hydrodynamic processes in annular space during stabilization system operation, that is change of fluid level above the pump depending on borehole conditions and design parameters of electric valve. Results. Effect of parameters of the bypass valve – the diameter of flow section and length on dynamics of change of a liquid level above the pump, as well as the impact of liquid properties, namely its viscosity on intensity of restoration of a liquid level above the pump was studied. It was found that when the diameter of the electrical valve is increased, more intensive restoration of the liquid level above the pump is observed due to the reduction of hydraulic resistance in the valve cavity. Similarly, it was found that with increase of electrical valve length, as well as with increase of viscosity of liquid, coefficient of flow and intensity of liquid level recovery above the pump decreases respectively.

Optimization of the Well Start-Up Procedure and Operating Parameters for ESP Gas Well Dewatering

The Electrical Submersible Pump (ESP) systems were deployed in two gas wells for the dewatering of the gas reservoir. However, problems, such as the failure to start up the ESP, and changes in reservoir parameters occurred during the production. For the first problem, the well start-up operation records indicate that the ESP’s gas locking happened. To avoid this, an optimization method of the well start-up procedure for the ESP well with a check valve was correspondingly proposed, which can solve the problem without any workovers. Secondly, based on the working characteristics of the ESP and the nodal analysis method, a set of optimization methods for the operating parameters of ESPs were introduced to achieve the inflow and outflow balance. For one well, the original ESP system was planned to be installed after hydraulic fracturing. Traditionally, the ESP operating parameters were designed based on the production rate. However, in this case, the production rate and the ESP operating frequency were designed simultaneously to maximize the pump efficiency.

Influence of groundwater extraction on rock filtration properties in the territory of the Latitudinal Ob region

The problem of groundwater protection in areas, where oil and gas production is taking place, is especially important today. The article focuses on the impact of groundwater extraction on the state of the filtration medium in small water bodies. Studies including hydrodynamic testing (cluster pumping) were being carrying out from 9 years at the same site. As a result of three exper-iments, experimental data were obtained, and then were interpreted in the framework of the Hantush model. The parameters of the aquifer are determined: coefficient of water conductivity and pressure conductivity factor, overflow factor, overflow coefficient. The article gives an analysis of changes in reservoir parameters. As a result, it was found that the long-term operation of ground-water in small water bodies also leads to an improvement in the state of the filtration medium, as well as in large deposits of fresh groundwater. It should be emphasized that in conditions of continuous extraction of groundwater the subsoil user should pay special attention to groundwater monitoring, namely, hydrodynamic studies, the results of which determine the hydrogeological parameters of the reservoir, and their changes indicate the state of the filtration medium.

The study of reservoir parameters of subsurface rocks based on the core data of anticline belt of Sangachal-deniz–Bulla-deniz

Alongside the geological-geophysical characteristics of the fields being developed and explored, the calculation of hydrocarbon reserves, the modeling of the fields, as well as the specification and direction of a new exploration are of great importance with regard to the study of their reservoir parameters. With this purpose, the geological-geophysical studies carried out in the anticline belt of Sangachal-deniz–Bulla-deniz, and the data of samples of subsurface rocks from well intervals have been analyzed as well. The changes in reservoir parameters of the rocks of various granulometric content in the anticline zone have been investigated and the graphs of parameters depending on the depth have been developed. The studies justify that the sand and sand deposits keep their reservoir parameters even in comparatively large depths. These characteristics indicate the presence of favorable litofacies and structural-petrographic conditions for the accumulation of oil and gas reserves in deep sections.

Sensitivity analysis of effective fluid and rock bulk modulus due to changes in pore pressure, temperature and saturation

Fluid substitution plays a vital role in time-lapse seismic modeling and interpretation. It is, therefore, very important to quantify as exactly as possible the changes in fluid bulk modulus due to changes in reservoir parameters. In this paper, we analyze the sensitivities in effective fluid bulk modulus due to changes in reservoir parameters like saturation, pore-pressure and temperature. The sensitivities are analyzed for two extreme bounds, i.e. the Voigt average and the Reuss average, for various fluid combinations (i.e. oil–water, gas–water and gas–oil). We quantify that the effects of pore-pressure and saturation changes are highest in the case of gas–water combination, while the effect of temperature is highest for oil–gas combination. Our results show that sensitivities vary with the bounds, even for same amount of changes in any reservoir parameter. In 4D rock physics studies, we often neglect the effects of pore-pressure or temperature changes assuming that those effects are negligible compare to the effect due to saturation change. Our analysis shows that pore-pressure and temperature changes can be vital and sometimes higher than the effect of saturation change. We investigate these effects on saturated rock bulk modulus. We first compute frame bulk modulus using the Modified Hashin Shtrikman (MHS) model for carbonate rocks and then perform fluid substitution using the Gassmann equation. We consider upper bound of the MHS as elastic behavior for stiffer rocks and lower bound of the MHS as elastic behavior for softer rocks. We then investigate four various combinations: stiff rock with upper bound (the Voigt bound) as effective fluid modulus, stiff rock with lower bound (Reuss bound) as effective fluid modulus, soft rock with upper bound as effective fluid modulus and soft rock with lower bound as effective fluid modulus. Our results show that the effect of any reservoir parameter change is highest for soft rock and lower bound combination and lowest for stiff rock and upper bound combination.

A review on time-lapse seismic data processing and interpretation

Time-lapse (TL) seismic or 4D seismic has great potential in monitoring and interpreting time-varying variations in reservoir fluid properties during hydrocarbon production. The TL surveys interpret dynamic changes in reservoir parameters by detecting differences in seismic responses from different vintages, which are obtained by repeated seismic surveys over the same area. For a proper and more precise quantitative interpretation of the TL seismic responses, TL seismic processing enhances repeatability of the TL-data sets, and thus reduces artificial differences that come from unavoidable differences in repeated-seismic-survey environments. This study aims to bring an insight to the state of the art in both TL seismic data processing and interpretation by reviewing previously-published researches. TL data processing is a sequential process conducting 4D binning and simultaneous 4D pre-stack processing; 4D binning improves spatial repeatability while “simultaneous 4D pre-stack processing” derives common processing operators employing cross-equalization (XEQ) as a core technique. TL seismic interpretation is categorized by the characteristics of data being interpreted into two strategies: interpretation of data sets from all TL vintages and interpretation of differences in seismic data between vintages.

A preliminary study on sensitivity of seismic responses to changes in reservoir parameters using various RPM-constructing strategies

Rock physics model (RPM) transforms reservoir characteristics into elastic seismic properties which control generation of seismic responses through synthetic seismic simulation. The changes in fluid saturation or pressure lead to corresponding changes in seismic responses based on constructed RPM. The different RPMs are first constructed based on four different strategies of Gassmann's equation, Krief's formulation, Duffy–Mindlin's method, and Wyllie's equation. Differences among these RPMs are analyzed before performing sensitivity analysis of changes in seismic responses with respect to changes in reservoir parameters. The synthetic seismic responses used for the analysis are generated from the seismic simulation, which algorithm is developed by using a finite difference method based on staggered grid with convolutional perfect match layer and free surface.

Fast History Matching of Finite-Difference Models Using Streamline-Derived Sensitivities

Summary We propose a novel approach to history matching finite-difference models that combines the advantages of streamline models with the versatility of finite-difference simulation. Current streamline models are limited in their ability to incorporate complex physical processes and cross-streamline mechanisms in a computationally efficient manner. A unique feature of streamline models is their ability to analytically compute the sensitivity of the production data with respect to reservoir parameters using a single flow simulation. These sensitivities define the relationship between changes in production response because of small changes in reservoir parameters and, thus, form the basis for many history-matching algorithms. In our approach, we use the streamline-derived sensitivities to facilitate history matching during finite-difference simulation. First, the velocity field from the finite-difference model is used to compute streamline trajectories, time of flight, and parameter sensitivities. The sensitivities are then used in an inversion algorithm to update the reservoir model during finite-difference simulation. The use of a finite-difference model allows us to account for detailed process physics and compressibility effects. Although the streamline-derived sensitivities are only approximate, they do not seem to noticeably impact the quality of the match or the efficiency of the approach. For history matching, we use a generalized travel-time inversion (GTTI) that is shown to be robust because of its quasilinear properties and that converges in only a few iterations. The approach is very fast and avoids many of the subjective judgments and time-consuming trial-and-error steps associated with manual history matching. We demonstrate the power and utility of our approach with a synthetic example and two field examples. The first one is from a CO2 pilot area in the Goldsmith San Andreas Unit (GSAU), a dolomite formation in west Texas with more than 20 years of waterflood production history. The second example is from a Middle Eastern reservoir and involves history matching a multimillion-cell geologic model with 16 injectors and 70 producers. The final model preserved all of the prior geologic constraints while matching 30 years of production history.

Pressure and fluid saturation prediction in a multicomponent reservoir using combined seismic and electromagnetic imaging

This paper presents a method for combining seismic and electromagnetic (EM) measurements to predict changes in water saturation, pressure, and CO2 gas/oil ratio in a reservoir undergoing CO2 flood. Crosswell seismic and EM data sets taken before and during CO2 flooding of an oil reservoir are inverted to produce crosswell images of the change in compressional velocity, shear velocity, and electrical conductivity during a CO2 injection pilot study. A rock‐properties model is developed using measured log porosity, fluid saturations, pressure, temperature, bulk density, sonic velocity, and electrical conductivity. The parameters of the rock‐properties model are found by an L1‐norm simplex minimization of predicted and observed differences in compressional velocity and density. A separate minimization, using Archie's law, provides parameters for modeling the relations between water saturation, porosity, and electrical conductivity. The rock‐properties model is used to generate relationships between changes in geophysical parameters and changes in reservoir parameters. Electrical conductivity changes are directly mapped to changes in water saturation; estimated changes in water saturation are used along with the observed changes in shear‐wave velocity to predict changes in reservoir pressure. The estimation of the spatial extent and amount of CO2 relies on first removing the effects of the water saturation and pressure changes from the observed compressional velocity changes, producing a residual compressional velocity change. This velocity change is then interpreted in terms of increases in the CO2/oil ratio. Resulting images of the CO2/oil ratio show CO2‐rich zones that are well correlated to the location of injection perforations, with the size of these zones also correlating to the amount of injected CO2. The images produced by this process are better correlated to the location and amount of injected CO2 than are any of the individual images of change in geophysical parameters.

Three-Dimensional Seismic Evaluation of Reservoir Continuity and Four-Dimensional Seismic Monitoring of an EOR Process: ABSTRACT

The technology of three-dimensional reflection seismology has developed to the point where detailed mapping of some reservoir characteristics can be done in manner useful to field development. Two examples of the analysis of high-resolution seismic data for reservoir studies are presented here. In the first example, the reflection trace amplitude and the calculated seismic attributes of a three-dimensional survey delineate a discontinuous section of reservoir sand and effectively map sand thickness. When local structure is statically removed from the seismic data, time slices through the three-dimensional data volume are interpreted as horizon slices. By correlation of subsurface well information with seismic character, variations in seismic attributes on the horizon slices are interpreted as maps of lateral changes in reservoir parameters. The second example shows the results obtained using three-dimensional seismic data to monitor the progress of an in-situ fireflood test. Three sets of three-dimensional seismic data were recorded in an identical manner over the test area during a 1-year period. Taken as a whole, the seismic data have a fourth dimension, calendar time. By comparison and direct integration of the data sets, it is possible to map the propagation of the fireflood in the reservoir over time and calculate amore » net burn thickness map from seismic amplitudes calibrated with post-burn core information. These examples are from small reservoir tests related to the EOR pilots, but as the results imply, the same combinations of three-dimensional seismic and subsurface well control can be applied to large-scale field development.« less