Search

Summary A significant amount of oil is contained in carbonate reservoirs, but only half of that oil can be produced by secondary enhanced oil recovery (EOR) methods. However, substantial improvements were made in EOR techniques and the prediction of carbonate reservoir performance within the last decades. Nevertheless, existing flow-simulation computer programs failed to provide a reliable prediction of such reservoirs due to their high heterogeneity and the reactivity of the rock. Potentially, in-situ combustion (ISC) is considered effective in developing heavy oils in carbonate reservoirs. The combustion reactions between crude oil and heterogeneous rock matrices introduce additional complexity to the simulation process. Also, most of the laboratory experiments studying the reaction kinetics of the ISC process are performed on the crushed core. However, to minimize the risks, improve the control of the process, and overcome upscaling issues, physical simulation must be carried out under conditions as close to the reservoir as possible. Consolidated core material in combustion tube (CT) experiments is desirable for better simulating some reservoir conditions with synthetic packs and for the cases when actual preserved reservoir core material may be available. Studying the relative effects of porosity and packing properties (specific surface area, sand grain distribution, and cementation) on the fuel is essential to evaluating the process under actual field conditions. This work presents a set of medium-pressure CT (MPCT) tests on crushed and consolidated cores and analyzes the differences, limitations, and performances of both approaches. Two MPCT tests were performed to evaluate the ISC feasibility on the heavy-oil carbonate reservoir with an initial oil saturation level of 0.38 to 0.50. According to previously published experimental results, such oil saturation levels can help avoid oil banking. Both experiments were conducted at reservoir conditions to consider the phase behavior at elevated pressures and temperatures. The method used in this research allows approbation of the methodology of ISC tests using consolidated core at high pressure, ensuring pack and process integrity during the experiment. The influence of consolidated core caused by significantly lower porosity and more uniform porous media elements than those made with unconsolidated material on combustion performance was assessed. Valuable data for different variations of combustion experiments were generated. This work compared two tests and presented the combustion parameters for a stabilized combustion period, such as fuel and air requirements, recovery efficiency, front velocity, and composition of produced gases. The research intends to demonstrate the potential application problems and address issues that might arise during ISC application on target reservoirs, including the higher air flux required for lower porosity of consolidated core samples. The experimental results performed under conditions closest to reservoir conditions are essential for further predictions and affect the ISC performance during pilot tests.

The theoretical principles of the laboratory methods for studying the wettability of unconventional oil formation rocks are discussed and examples of their practical implementation are presented. The comparative analysis of the advantages and disadvantages of each method is presented. It is shown that despite the recent progress in the development of methods for determining the wettability of rocks, they still need to be improved. Examples of their possible improvements are discussed.

Rock swelling and rock disintegration in the presence of drilling, stimulation and completion fluids are considered to be the main reasons for operational and production problems for wells in clay-rich formations. The impact of these fluids on rock properties shall be established for the effective treatment design. This paper describes the development of the experimental setup for studying rock swelling in reservoir conditions and the application of this setup for the evaluation of swelling mechanisms of shale rock samples. Swelling quantification was performed using measuring piston displacement that was caused by rock swelling in a piston accumulator during pressure maintenance. We studied the interaction of the disintegrated rock samples with water-based and hydrocarbon-based fluids and supercritical CO2. It was found that alkaline water solution in reservoir conditions causes swelling of the used rock samples in the amount of 1–3% vol. with a direct correlation between the rock swelling magnitude and the total clay content. The change in the rock volume in the presence of the used hydrocarbon-based fluid depends on the content of organic matter, its distribution in the rock, and the clay content. The observed swelling degree in the hydrocarbon fluid and CO2 was significantly lower (0–0.5% vol.) than in water. The proposed methodology and obtained results can further be used for the optimization of various operations in clay-rich formations.

Air injection has immense potential for hydrocarbon recovery from various reservoirs. One of the screening techniques which can be applied to evaluate a candidate oil for the air injection process is the accelerating rate calorimeter (ARC). The unique feature of this instrument is that it can provide adiabatic conditions and handle experiments at high pressures. This paper reviews four tests performed in closed and flowing ARCs to fingerprint and observe the thermal behavior of a crude oil. The crude oil used for this study is characterized as a 19.3°API and viscosity of 710 mPa.s at 21°C. The oxidation experiments were performed under two scenarios of oil-only and oil in the presence of native carbonate core. Initial starting conditions of each test were at a temperature of 23°C and a reservoir pressure of 13.8 MPa. Flowing ARC experiments showed that Low-Temperature Oxidation occurs at a temperature of about 150°C, whereas ignition occurs at about 350°C when High-Temperature Oxidation region was dominant. However, when using the closed ARC, the thermal behavior of the studied oil appeared to have different temperature characteristics, and the onset of the maximum self-heat rate occurred at temperature of 288°C. The effect of the vapor phase combustion as well as the calculation of kinetic parameters are also discussed in this work.

In this work an improved method of polychromatic X-raying for samples of composite structure is offered. During image processing, the exact spectral characteristics of source, detector and substances are taken into account, and the digital filtration of stray signals from scattered radiation is applied. From the experimental data, with the help of detector and calibration media spectra, the spectral structure of radiation for pulse X-ray devices with a cold cathode is determined. Use of the developed techniques allows one to reduce the number of calibrations, increase the accuracy of measurements of quantity for each component, and determine the quantitative distribution of different substances in space by the reduced number of images.

Short description of the Electron KRT system and its performance is given. Functional capabilities of the system are considered on the basis of the accumulated operating experience.

Obtaining the relperm curves as a result of multiphase flow calculation immediately in the porous media can be of current interest. Some researches have been carried out to date where relperms are derived by solving the Navier–Stokes equations for communicating pore channels. Those approaches have two significant drawbacks: (1) need to reconstruct the pore space based on the core CT scanning, and (2) intensive work for solving the Navier–Stokes equation system which requires supercomputers. The results of our work help to compute relperm curves using normal computers. We were able to do this due to several factors: (1) simplified pore space reconstruction based on capillary curve data, (2) using the flow-cluster notion as an element that averagely describe the pore space geometry, and (3) using the Bernoulli generalized two-phase flow equation. This approach helped to compute the relperm curves within plausible timing and compare them with actual test curves. We demonstrate that a material factor to affect the relperm curve shape is the pressure loss due to interfacial forces. We propose the empirical functions and parameters to simulate those effects. The computed relperm curves show a pretty good match with the actual test results.