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CO2 mobility control in porous media is crucial to geological sequestration of CO2 and enhanced oil recovery (EOR). Although aqueous foam has been widely used to control the mobility of CO2, bubble...

The performance of polymer gel to plug a hydraulic fracture is greatly affected by its distribution patterns and gelling effect. In this study, the migration of a gel plugging agent in a fracture and its plugging after gelling were investigated by physical simulation experiments. In addition, the distribution patterns of the gel plugging agent and its plugging mechanism after gelling were investigated in detail. The results of this study revealed that the migration flowing behavior of the gel solution in a fracture can be divided into three streams: fracture flow, leak off flow, and matrix flow. Such behavior distributed the gel in three different patterns after gelling: gel clusters in the fracture, gel layer on the fracture surface, and dispersed gel lumps in the matrix pores-throats. Because of the leak off flow and the difference in components, the gel solution has apparent disproportional leak off–diffusion of components during its migration in a fracture, with less polymer molecules and loss of more cross-linking agent ions. The leak off of the cross-linking agent significantly deteriorates the gelling strength of the polymer gel, affecting its performance to plug a hydraulic fracture. The results also show that when the normalized concentration of the cross-linking agent ions in a fracture is less than 0.6, gel fails to plug the fracture effectively after gelling. When gelling was carried out by in situ cross-linking, polymer gel provided more satisfactory plugging performance than the gelling via ground pre-cross-linking.

CO2-responsive smart fluids have been widely investigated in the past decade. In this article, we reported a CO2-responsive smart fluid based on supramolecular assembly structures varying from vesicles to wormlike micelles.

A zwitterionic surfactant, hexadecyl hydroxypropyl sulfo betaine, was examined for its ability to stabilize supercritical CO2 (SC-CO2) foam, with the goal of improving the oil recovery from mature ...

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Underground cross-linking profile control and water shutoff and deep fluid flow to chemical agent system are usually composed of main agent, cross-linking agent and additives. The cost of cross-linking agent and additives generally accounts for 30–50% of the total cost of the system. Many inorganic salt ions are widely used as cross-linking agent or additives. In this paper, using Ca2+ and Mg2+ scale forming ion source in CaCl2 water type oilfield high salinity formation water (as water injection) as crosslinking agent, cross-linking of original inorganic microgel is carried out to reduce the cost of steering agent. The formation of nano microscale inorganic microgel with density similar to that of environmental water source can be formed by cross-linking of the steering agent with scale forming ions in formation water. The microgel can be dispersed or suspended in water, and gradually adsorbed on the rock skeleton of the dominant channel such as hole or crack to form a micro gel coating in order to narrow the flow dominant channel and form resistance to flow. The passage of plugging does not die, achieving the purpose of adjusting the dominant channel, expanding the volume and improving the efficiency of water flooding. At the same time, the particle size of the micro gel can prevent it from entering the low permeability matrix to contaminate the oil layer. The diversion agent has the characteristics of rapid dissolution, temperature resistance, salt resistance, environmental protection, long-term effectiveness and no construction risk. Field tests of deep profile control and flooding have been carried out in reservoirs with different temperature and salinity at home and abroad. After profile control diversion in test blocks or well groups, the effect of improving water flooding is good. The average increase of water injection pressure is 2–3 MPa, and the effective rate of increasing oil production and precipitation in oil wells is more than 80%, and the validity period is less than one year up.

High temperature-resistant polymer (HTP) was synthesized by in-situ cross-linking of interpenetrating reaction using H-2 monomer containing amide bond and H-1 molecule containing hydroxyl as raw materials. IR spectra result showed that there were characteristic functional groups of H-1 and H-2 cross bond at the same time, that was to say that H-1 cross-linking reaction and H-2 polymerization could simultaneously take place. The interpenetrating cross-linking structure, extension properties at room temperature and long-term heat resistance properties of the material were tested. The experiment results showed that in the whole range of observations, HTP material cross-links and interpenetrates uniformly. The SEM pictures confirmed the interpenetration structure of HTP material. After cross-linking and interpenetration, the scale of HTP structure became smaller than before. This material had tensile resistance, dispersion stability in water, volume expansion, and could reach the maximum swelling ratio of 1.69 within 1.5 h at room temperature. At 90 °C, 120 °C and 140 °C, after soaking 130 days in formation water, HTP volume reduction rate was 1.57%, 3.24% and 6.82%, respectively.

Aiming at deep profile control in water flooding reservoirs, a heterogeneous combination flooding system, composed of dispersed particle gel (DPG) and a zwitterionic surfactant (THSB), was developed. The mean particle diameter was adjusted and then the DPG morphology and diameter were characterized using a laser scanning, confocal microscope, and dynamic light scattering. The effects of DPG concentration, temperature, pH, and salinity on THSB interfacial tension (IFT) were investigated. A method for determining DPG concentration was proposed, and the dynamic retention and migration mechanisms of the particles were evaluated, using cores with different permeabilities. Finally, the oil displacement mechanism of the combination flooding system was explored through visual simulation experiments and scanning electron microscopy. The results showed that the particle diameter was 2.5 μm, that compared with a surfactant system, the IFT of the combination flooding system was relatively low, and that the temperature, pH, and NaCl content of solutions had little effect on THSB IFT. Since specific matching relationships between DPG particles and reservoir pore throats existed, the retention amount and injection pressure were improved with the increased core permeability. Visual simulation experiments revealed the oil recovery mechanism of the combination flooding system. This combination flooding system can be used in reservoirs under varied conditions, as the particle diameter can be adjusted on a case-by-case basis, and the THSB surfactant proved to be high-temperature resistant and high-salinity tolerant. The combination flooding system can be applied to deep profile control and oil displacement, in oil fields.

A novel mixed-mode monolithic stationary phase based on bonding of 4,5-imidazoledicarboxy acid to the surface of an organic-silica hybrid monolith was prepared and characterized. Satisfactory characteristics in terms of mechanical stability, permeability and reproducibility of the resultant monolithic column were achieved. A typical per aqueous chromatographic behavior was observed in water-rich mobile phases. The resultant monolithic column was applied for the efficient resolution of various polar and hydrophilic compounds under per aqueous or reversed-phase chromatographic conditions, which successfully demonstrated its suitability for the analysis of these polar compounds in highly aqueous mobile phases. The highest column efficiency obtained for the amines was 149 000 N m−1. The experimental results showed that the mixed-mode mechanism of hydrophobic and ion-exchange interactions was involved in the separation under the given conditions. The successful applications suggested that the mixed-mode organic-silica hybrid monolithic column could offer a wide range of retention behaviors and flexible selectivities toward polar compounds, achieving various target separations.

The inorganic gel coating diverting agent, which is non-toxic and environmentally friendly, is developed for in-depth water diversion to improve water flooding effect. After being injected into the formation, the agent reacts with the formation water and forms inorganic silicate gel with a density approximating to formation water. The gel suspends in water as a bulk or particulates, scales and forms inorganic gel coating on rock surface by way of adsorption. The dominant channels of deep formation water are narrowed, forming flowing resistance and forcing flow diverting of the subsequent fluid so as to improve water flooding effect. This agent features fast solution, temperature resistance, salt resistance, environmentally friendly, and long-acting. It has been used in different reservoirs with different temperatures and salinity conditions, such as the Lunnan Oilfield of the Tarim Basin, the Yuejin oil region of the Qaidam Basin, and the Dagang Oilfield for in-depth flow profile control. The field applications involve single well group and whole block, with success ratio up to 100%, average injection pressure of well group increasing by 2–3 MPa, and the effective rate of oil production increase and water-cut decrease of producers are over 80%. Key words: in-depth profile control, diverting agent, inorganic gel, coating, field test, effect analysis

The effect of a polymer on chromium diffusion during gelant injection into fractured media was explored with a polymer/chromium(III) (Cr3+) gelant. The capture and barrier effects are two main affecting mechanisms of polymer molecules on the diffusion of Cr3+, and the formation of the polymer leak-off layer is a key influencing factor. The experimental results show that when the polymer molecular weight (MW) or concentration increased, both the diffusion rate of Cr3+ and the leak-off degree of the gelant decreased sharply. This resulted in the delayed initial production and advanced final production of Cr3+. Because of the changing diffusion rate of Cr3+ and the dilution effect of brine during gelant injection, the change trends of the Cr3+ production from the fracture outlet and matrix ports reversed after the injection volume exceeded a value; this value was named the critical injected volume. During gelant injection into the fractures, under the effects of gravity action and the disproportionate diffusion of Cr3+, the chromium diffusion profiles measured at the fracture top and bottom were different. The chromium diffusion profile along the matrix varied with increasing gelant injected volume, but it finally reached the diffusion equilibrium state in the matrix. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43447.

This paper describes the applications of annular chemical packer (ACP) with highly tailored thixotropic characteristics in horizontal wells completed with slotted liners. The purpose of the applications was to provide a cost effective annular isolation method for water control in horizontal sections. The rheological properties of ACP, the placement techniques of ACP, the subsequent treatment procedures, and the uncertainties involved were provided. The oil rate of the candidate onshore horizontal well M28-P7 was only 0.5m3/d, with 99% water cut. Production logging identified that about 86% of liquid rate was produced from the toe section. The ACP was placed across the shale between the two different liquid-producing zones, and a mechanical plug was dropped at middle of the ACP site. Then effective acidizing was performed for the heel section in order to gain higher permeability. After the treatments, the water cut decreased to 83% while the corresponding oil gain reached up to 5.3m3/d, 20 times that of the pre-treatment scenario. The other similar treatment was performed in offshore horizontal well A2h after production logging. Two ACP plugs were designed and an optimized recompletion string was put into the well. The water control operation went smoothly, which significantly decreased the water cut to 3% from 74% and the oil rate was increased to 187m3/d, with the net oil increased by about 100m3/d over the pre-treatment scenario. This is the first ever successful water control operation with water diagnosis in an offshore well with a tough completion in the South China Sea. Case histories indicate that using ACPs was the right choice for blocking water in the sand screen liner completion with high level technical success and economic feasibility. Also a comprehensive and detailed water control design based on production logging results, completion, and reservoir permeability distribution is the key for successful water shutoff.

Due to severe heterogeneity of thick positive rhythm reservoir and the gravity influence, the injected water channels and ineffectively cycles in high-permeability layers at the bottom of thick reservoir. An innovative in-depth fluid diversion technique, gel barrier placement, will be a promising approach to tap the potential of remaining oil in positive rhythm reservoirs in the period of high water-cut, which involves injecting gel into the radial laterals in the vertical wells between the injectors and producers to form ‘gel barriers’, then follow-up injected water will bypass these barriers and be diverted into the upper low permeability zones where the remaining oil is relatively enriched. As a result, the sweep efficiency of the upper low-permeability zones can be increased. A pilot of gel barrier placement was conducted in Daqing oil field. The paper deals with well pattern and chemical agents’ selection, injection scheme design, numerical simulation, and field implementation results.

Abstract Due to severe heterogeneity of thick positive rhythem reservoir and the gravity influence, the injected water channels and ineffectively cycles through its lower high permeability zones. For the whole reservoir, its sweep efficiency is relatively low and a huge amount of residual oil is enriched in its upper low permeable zones. The technique of in-depth fluid diversion by "gel dam" placed with horizontal well involves the injection of gel by horizontal or sidetracking wells drilled between the injection and production wells in the lower more permeable and strongly swept zones of thick positive rhythm reservoir, creating" gel dams". The injected water then will bypass the "gel dams" and be diverted into the upper low permeability zones where crude oil is relatively enriched. As a result, the sweep efficiency and oil recovery of the upper, low permeability zones can be both increased. In this paper, the EOR mechanism of the technique is studied by means of laboratory water flooding experiment combined with x-ray computer tomography(C T). The physical model, an artificial cementing heterogeneous model casted with epoxy resin on surface, is made based on the similarity criteria for water flooding process in 2D porous media. The water flooding processes in the physical model, before and after the "gel dam' is formed, are scanned by x-ray C T at different pore volume injected, which provides a visible means for studying the EOR mechanism of the technique, through observing the distribution feature of "gel dam', tracking the oil and water distribution, water flooding streamline's change, fluid saturation distribution and its dynamic variation. The results of water flooding experiments indicate that, with this technique, the injected water is diverted into the upper low permeability layer to displace the remaining oil therein, and the sweep efficiency and oil recovery both increase significantly. After the "gel dam" formed, the ultimate oil recovery increases by 16.7%, its water cut falls to 62.8%, and its ascending velocity slowed down. With" gel dam" technique, gel can be placed in the deep reservoir zone to achieve in-depth fluid diversion. It will be a promising EOR method for thick positive rhythm reservoir.

Abstract In view of the ineffective cycling issue of injected water through the high permeability zones during water flooding process in positive rhythm reservoirs, the gel dam in-depth fluid diversion technique is proposed. The technique first promoted the injection of gel by horizontal or sidetracking wells drilled in the more permeable and strongly swept zones of thick positive rhythm reservoirs. The injected water then will bypass the "gel dams" and be diverted into the upper unswept or poorly swept low permeability zones. As a result, the swept efficiency and oil recovery of the upper low permeability zones can be both increased. Gel dam placement method can be enhanced the oil recovery both in the laboratory experiments and numerical simulation technology, but the use of new drilling horizontal wells for gel dam placement accompany with certain technical and economic risks; In order to reduce risk, to explore the law of horizontal well gel dam placement, we proposed the use of the crossing straight well set to place the gel dam for Daqing Oilfield, which is consistent with the current research status. Straight and horizontal wells gel dam placement have the similar principles, but there are some differences, how to use a crossing well to place the gel dam should be further study to improve the development effectiveness. The physical modeling experiments of gel dams in a positive rhythm formation and in a point bar sand body are conducted in the 3D physical model. The results of the experiments indicated that, with one or two gel dams, the sweep volume and ultimate oil recovery were both increased greatly, and the water cut ascending velocity was decreased. Compared with the physical model with horizontal gel dam, the ultimate oil recoveries of those with gel dams decrease by 8.1,but the oil recvoery is still 7.6% higher than waterflood. By vertical well "gel dam" in-depth fluid diversion technique, the difficulties in the in-depth placement of plugging agents will be solved, risk has been reduced and the swept efficiency of positive rhythm reservoir can be increased significantly.