• Energy Research

Cyclic steam stimulation is an effective thermal recovery method for heavy oil recovery. The key potential mechanism is the growth of the steam chamber after steam injection. Taking the LD5X heavy oil reservoir as an example, besides the interlayer developed in this area, the top water and bottom water distribute above and below the interlayer. These factors may have adverse effects on the development of the steam chamber, thus affecting the final heavy oil exploitation. In this work, our goal is to study the effects of interlayer permeability and well–interlayer distance on CSS performance (in the presence of top and bottom water). We developed a high-temperature-resistant interlayer. Based on the simulated interlayer, the field scale model was converted into a laboratory element model through the similarity criterion. In order to quantitatively evaluate the performance of steam stimulation, a thermal detector was used to measure the dynamic growth of the steam chamber and record the production data. The experimental results show that the self-made interlayer has high-temperature resistance, adjustable permeability, and little difference between the physical parameters and the target interlayer. During the cyclic steam stimulation process, the steam chamber presents two different stages in the presence of the top water area, namely the normal production stage and the top water discharge stage. The bottom water has little effect on the growth of the steam chamber. The small interlayer permeability, the increase in horizontal well–interlayer distance, and the existence of the interlayer will delay the top water leakage during steam stimulation. This study has reference significance for us to develop heavy oil resources with a top water barrier when implementing steam stimulation technology.

Abstract Leakage risk assessment is an inevitable procedure in permanent sequestration and storage of CO 2 in deep saline aquifers and depleted oil and gas reservoirs, where the integrity of caprock is most critical. Low porosity and low permeability concrete cubes were employed as caprock analogs to investigate the supercritical CO 2 injection-induced fracturing processes under true tri-axial stress conditions. A systematic experimental procedure, consisting of active acoustic emission measurement, pressure decay, injection pressure and temperature monitoring, fracture coloring, and gas fracturing, is formulated to qualitatively and quantitatively characterize the injection-induced fracturing processes and fracture morphology. Occurrence of injection-induced fracturing can be directly identified from peaks of borehole pressure profiles as well as sharp drops on temperature profiles due to CO 2 expansion, but generally there was no fracture propagation plateau appearing for the 20 cm rock cubes with zero pore pressure. Acoustic wave signatures, including both waveform change and arrival time delay, can effectively capture the extension of induced fractures inside the opaque rock. Initiation and propagation of supercritical CO 2 injection-induced fractures are highly dominated by the tri-axial stresses, following the general trend of continuum mechanics at high stress levels with large stress difference. As the stress difference decreases, induced fractures branch off in relatively arbitrary directions. For these supercritical CO 2 injection-induced fracturing experiments, poroelastic mechanics model makes a decent fit with the measured breakdown pressure of the caprock analogs. Findings in this study are valuable for risk analysis and operation optimization of geological CO 2 sequestration and storage as well as for CO 2 fracturing design and implementation in shale and tight reservoirs.

Abstract Water flooding is an efficient approach to maintain reservoir pressure and has been widely used to enhance oil recovery. However, preferential water pathways such as fractures can significantly decrease the sweep efficiency. Therefore, the utilization ratio of injected water is seriously affected. How to develop new flooding technology to further improve the oil recovery in this situation is a pressing problem. For the past few years, controllable ferrofluid has caused the extensive concern in oil industry as a new functional material. In the presence of a gradient in the magnetic field strength, a magnetic body force is produced on the ferrofluid so that the attractive magnetic forces allow the ferrofluid to be manipulated to flow in any desired direction through the control of the external magnetic field. In view of these properties, the potential application of using the ferrofluid as a new kind of displacing fluid for flooding in fractured porous media is been studied in this paper for the first time. Considering the physical process of the mobilization of ferrofluid through porous media by arrangement of strong external magnetic fields, the magnetic body force was introduced into the Darcy equation and deals with fractures based on the discrete-fracture model. The fully implicit finite volume method is used to solve mathematical model and the validity and accuracy of numerical simulation, which is demonstrated through an experiment with ferrofluid flowing in a single fractured oil-saturated sand in a 2-D horizontal cell. At last, the water flooding and ferrofluid flooding in a complex fractured porous media have been studied. The results showed that the ferrofluid can be manipulated to flow in desired direction through control of the external magnetic field, so that using ferrofluid for flooding can raise the scope of the whole displacement. As a consequence, the oil recovery has been greatly improved in comparison to water flooding. Thus, the ferrofluid flooding is a large potential method for enhanced oil recovery in the future.