Junjian Li

Investigation on the Adaptability of the Polymer Microspheres for Fluid Flow Diversion in Porous Media

Large amounts of water producing from producers have been a great concern for petroleum engineers. In an attempt to inhibit water production and promote oil productivity, various water control agents and techniques have been devised for enhanced oil recovery purpose for decades with some good successes reported commercially. Mainly field-targeted specifically, however, these chemicals are limited in expansive reservoir applications for failing to tolerate harsh formation conditions of high temperature (HT) and high salinity (HS). Besides, their low injectivity is also another proper impediment. In this presentation, we synthesized a new agent of polymer microspheres using inverse emulsion polymerization technique to divert fluid patterns in deep porous media for reservoirs encountered recovery enhancement problems. These microspheres are made to tolerate HT and HS conditions, and can be pumped into deep pore space with relative ease. With the help of nuclear magnetic resonance (NMR) and nuclear pore membrane filtration techniques, a series of experimental procedures were conducted to test the adaptability of newly produced polymer microspheres to targeted pore structure in enhancing the sweeping efficiency of injection fluids. Both laboratory core tests and NMR data show good characteristics of polymer microspheres in modifying injection profile, demonstrating a good capability to divert fluid flow patterns in deep porous media and enhance oil productivity.

An Analytical Model for the Early Stages of Polymer Flooding

The threshold pressure gradient (TPG) was proved existent by laboratory experiments, and the relation between TPG and permeability is obtained. A new analytical method considering TPG, wellbore storage as well as skin effect for polymer flooding is presented. The results of the model are in good agreement with the field data. It is shown that the bottom-hole pressure differential is higher when considering TPG and the injective is reduced with the increase of TPG.

Research and Application on Resource Utilization Technology of Oily Waste Drilling Fluid

Abstract Oily waste drilling fluid is divided into two main types, oil based and oil mixed; each is included in the national list of hazardous waste because they contain oil, heavy metals, organic matter, and other pollutants. At present, waste drilling fluid is usually stored centrally or tightly closed all over the world, In this way, the pollutants are only sealed and isolated from the external environment but not completely eliminated and pose the risk of polluting the environment. Furthermore, re-injection into a formation or a landfill cannot recover the mineral oil and recycle the waste resources. This article proposes a technology of utilizing waste oily drilling fluid based on many tests and treatment options screening. The technology is chemical reaction-enhanced separation and hazard-free treatment. The obtained cleaner and the hazard-free treatment agent are added in the waste oily drilling fluid to recover the useful oil and make the remaining sludge less hazardous. The processed waste can be utilized to build cofferdam in the well site. The oil recovery ratio can be up to 85%. The compressive strength is moderate after addition of a hazard-free treatment agent. The product neither hardens soil nor affects the growth of plants; the oil, chemical oxygen demand (COD), heavy metals, and other pollutants in the leaching solution are lower than the second-level criterion in the Integrated Wastewater Emission Standard (GB8978-1996).

Further Insights into the Mechanism of Disproportionate Permeability Reduction

Disproportionate permeability reduction (DPR) is a phenomenon whereby many water-soluble polymer solution and polymer gels reduce the permeability to water flow more than to oil or gas flow. DPR is important for some gels that are applied to production wells in water-shutoff treatments. The mechanisms of DPR need more investigation and clarification. In this study, experiments on two different scales, coreand micro-model-scale, were conducted to study the mechanism of DPR in flow through permeable medium treated with Cr(III)-acetate-HPAM gels. The procedures for the two experiments can be similarly divided into five phases: gelant injection and gelation, oil flooding, gel rehydration with no oil phase pressure difference, oil re-flooding, and water flooding. In the core-scale experiments, we used nuclear magnetic resonance (NMR) to monitor the T2 signal change during fluorine-tagged oil and water flooding after the gel treatment. NMR can detect the signal change of trapped and free water inside the gel in different pore sizes in porous medium. In the micromodel-scale experiments, a microscopic glass-etched model is subject to red oil and blue water flooding alternately after the gel treatment. Oil extrusion under an oil phase pressure gradient and the evolution of oil flow channel are recorded by a video sensor. The subsequent water flooding is also investigated. Results show that a gel-displacement mechanism is a primary reason for the development of the oil flow path initially. As the displacement proceeds, the gel dehydration occurs induced by the oil phase pressure and therefore the flow channel continues forming, but no gel is produced during this phase. During gel rehydration, the flow channel is blocked, which can be inferred from the T2 spectrum and visual microscope image. However, the rehydrated gel can only partially reduce permeability and oil pathways re-establish easily with the subsequent oil flooding. In water flooding, water permeability decreases abruptly. The mechanisms for the disproportionate permeability reduction involve channel segregation, gel rehydration, residual oil effects, and the low permeability of gel relative to water.

In-depth Study of Using a Horizontal Well to Improve the Waterflooding Effect in an Old Oilfield via Physical Simulation

To understand deeply to mechanisms of improving recovery with horizontal well compared to vertical, a novel method is conducted to study it. A large scale artificial consolidated multilayer model is established according to the waterflooding scale criteria. Through it, effects of potential tapping with different methods are studied. The results show the effect of horizontal well tapping potential is better than vertical under major indicators; control ability of horizontal over remaining oil is stronger; that with an increase of water-cut, the degree of differentiation between sweep and displacement becomes smaller, and ratio of the two is always more than 1.

The Effects of Oil Displacement Efficiency and Conformance Efficiency on Viscosity of ASP Flooding in a Heterogeneous Reservoir

According to the formation conditions of alkali/surfactant/polymer (ASP) flooding in Daqing oilfield, the effects of the concentrations for polymer and alkali in ASP solution on oil recovery efficiency were studied by means of oil displacement experiments and numerical simulation. The effects on improving oil recovery by different ASP solution have been investigated from the aspects of interfacial characteristics and rheological behavior. Only the apparent viscosity of ASP solution reaches the critical viscosity, the ultralow interfacial tension can play an important role in enhanced oil recovery. Both displacement experiments and numerical simulation shows that ASP solution has a critical viscosity to certain heterogeneity.

Pore Network Modeling of a Polymer Flooding Microscopic Seepage Mechanism

Abstract Based on an oil-water two-phase pore network model, the authors provide a microscopic simulation model for polymer flooding together with a polymer flooding seepage mechanism. The authors also statistically analyze the laws of distribution of remaining oil after polymer flooding. On this basis, they study laws of distribution of retained polymer and its influence factors. The microscopic simulation showed that the remaining oil of network shape decreased significantly while the volume ratio of a single grain/island shape, fleck shape, and oil-water mixed shape increased. The retained polymer concentration in pores was inversely proportional to the product of the pore radius and the square root of shape factor.

Pore-scale study of the pressure-sensitive effect of sandstone and its influence on multiphase flows

The pressure-sensitive effect on the pore structure of sandstone was investigated using X-ray computed micro-tomography and QEMSCAN quantitative mineral analysis. In a physical simulation study, we extracted the pore network model from digital cores at different confining pressures and evaluated the effect of pressure sensitivity on the multiphase displacement process. In both the pore network model and QEMSCAN scanning, the pore structure was observed to be damaged under a high confining pressure. Due to their different scales, the pores and throats exhibited inhomogeneous changes; further, the throats exhibited a significant variation compared to that exhibited by the pores. Meanwhile, the heterogeneity of the pore structure under the two aforementioned activities was aggravated by the elastic–plastic deformation of the pore structure. The pressure-sensitive effect increased the proportion of mineral particles, such as quartz (the main component of the core skeleton), and reduced the proportion of clay minerals. The clay minerals were originally attached to the pore walls or interspersed in the pores; however, as the pressure increased, the clay minerals accumulated in the pores resulting in blockage of the pores. While simulating the multiphase displacement process, increasing the confining pressure was observed to severely restrict the flowability of oil and water. This study promises to improve the efficiency of reservoir development in terms of oil and gas exploitation.

Pore-Scale Imaging of the Oil Cluster Dynamic during Drainage and Imbibition Using In Situ X-Ray Microtomography

We imaged water-wet and oil-wet sandstones under two-phase flow conditions for different flooding states by means of X-ray computed microtomography (μCT) with a spatial resolution of 2.1u2009μm/pixel. We systematically study pore-scale trapping of the nonwetting phase as well as size and distribution of its connected clusters and disconnected globules. We found a lower , 19.8%, for the oil-wet plug than for water-wet plug (25.2%). Approximate power-law distributions of the water and oil cluster sizes were observed in the pore space. Besides, the value of the wetting phase gradually decreased and the nonwetting phase gradually increased during the core-flood experiment. The remaining oil has been divided into five categories; we explored the pore fluid occupancies and studied size and distribution of the five types of trapped oil clusters during different drainage stage. The result shows that only the relative volume of the clustered oil is reduced, and the other four types of remaining oil all increased. Pore structure, wettability, and its connectivity have a significant effect on the trapped oil distribution. In the water sandstone, the trapped oil tends to occupy the center of the larger pores during the water imbibition process, leading to a stable specific surface area and a gradually decreasing oil capillary pressure. Meanwhile, in oil-wet sandstone, the trapped oil blobs that tend to occupy the pores corner and attach to the walls of the pores have a large specific surface area, and the change of the oil capillary pressure was not obvious. These results have revealed the well-known complexity of multiphase flow in rocks and preliminarily show the pore-level displacement physics of the process.

An intelligent production fluctuation monitoring system for giant oilfield development

To guarantee production stability of oilfields, an intelligent production fluctuation monitoring and early warning system is developed based on methodologies of fuzzy comprehensive evaluation (FCE) and support vector machine (SVM). A novel early warning indicator system established through deep analysis of historical production data from Shengli oilfield is adopted in the FCE model and SVM model. Through performing field test, both the two models are proved to be capable of accurately predicting abnormal production decline of oilfields and the SVM model is proved to be of high prediction accuracy of 94%. Uncertainty analysis of early warning results can be realised in the system thanks to the mutual examination of the two models. This system also integrates modules of data reading, data processing, and result displaying, which facilitates application of it. The production monitoring and early warning system developed in this paper has been successfully applied in Shengli oilfield which is the second largest oilfield in China. It can play important role in ensuring production stability in oilfields, especially for giant oilfields and oilfields in high water-cut development stage.