In-depth Fluid Diversion Research Articles

Numerical Simulation Study on Parameter Optimization of In-depth Fluid Diversion in Low-permeability Fractured Reservoir

Daqing Chaoyanggou Oil Field is a low-permeability fractured oil reservoir that has entered into the middle and high water-cut periods of waterflooding extraction. Now, the moisture content is 74.88% and the injected water flows along fractures. The moisture content of oil wells increases quickly, accompanied with relatively serious invalid waterflooding. The in-depth fluid diversion can be used to exploit residual oil in substrate effectively and thereby increase recovery efficiency of the low-permeability fractured oil reservoir. In this study, parameters of in-depth fluid diversion in low-permeability fractured reservoirs can be optimized by numerical simulation method. According to geologic characteristics and fracture development situations in the study area, a geologic model of the study area was constructed. A historical fitting of exploitation indexes was carried out to optimize the dosage, injection rate and injection time of control-displacement agent during in-depth fluid diversion. Results demonstrated that the optimal dosage, the optimal injection rate and the optimal injection time of the control-displacement agent were 0.1 ∼ 0.15PV, 0.03 ∼ 0.04PV/a and about 70% of comprehensive moisture content, respectively. This study can provide reference to residual oil recovery in low-permeability fractured reservoirs during middle and high water-cut periods.

Kinetics and equilibrium of nanogel adsorption and desorption on sandstone

Polymer nanogels, elastic nanospheres with 3D network structure, have been recognized as promising materials to enhance oil recovery because they are designed to transport in deep of reservoirs for in-depth fluid diversion. Although conventional hard nanoparticles have been intensively investigated, the dynamic adsorption and desorption of elastic polymer nanospheres in porous media are still unclear, causing the uncertainty of applying them in the deep of reservoirs. In this work, we conducted circulation flowing experiments and post water flooding experiments to investigate the dynamic adsorption and desorption of nanogel in sandstones. Through UV–vis spectrophotometer, we found that nanogel exhibited rapid adsorption and desorption at the initial stages, but they have a long tail to reach equilibrium, in which the adsorption density distributed from 0.083 to 0.435 mg/g. The adsorption of nanogel increased with their concentration and core permeability, as well as salt concentration. However, salinity played a more important role during the desorption process due to the strong interaction between nanogel and sandstones. We also calculated the adsorption layer thickness, which ranges from 0.67 to 2.14, the results suggested that most of nanogel adsorption are multilayered processes. And the adsorption kinetics were fit by empirical equations, including pseudo-first order and pseudo-second order. The fitting comparison showed that the pseudo-first-order model is better suited for extreme low or high salinity (0.05% and 10% NaCl), while the pseudo-second-order model is preferred for moderate salinity (1% NaCl). These findings provide valuable insights for the effective placement of nanogel in oil recovery processes.

The oil/water interfacial behavior of microgels used for enhancing oil recovery: A comparative study on microgel powder and microgel emulsion

Microscale crosslinked polymeric hydrogels, termed microgels, have attracted considerable attention as enhancing oil recovery (EOR) agents due to their favorable in-depth fluid diversion effect. However, the oil/water interfacial behavior of microgels remains unclear, limiting the comprehensive understanding of the EOR mechanism. In this study, the oil/water interfacial behavior of microgel powder (MP) and microgel emulsion (ME) was studied through emulsification tests and interfacial tension (IFT) measurements. Despite the similar properties of the microgel particles, such as morphology, size distribution and zeta potential, ME exhibited better emulsification performance than MP in deionized (DI) water due to the presence of additional surfactants in ME. However, since the competitive adsorption between the microgel particles and surfactants on the oil/water interface changed with salinity, ME exhibited a higher emulsion volume but lower emulsion stability than MP in brine. Moreover, W/O and O/W emulsions were formed in DI water, but only an O/W emulsion was formed in brine for ME. Furthermore, MP exhibited better IFT reduction performance in brine due to the weaker steric hindrance and tighter adsorption layer on the oil/water interface. In contrast, ME showed better IFT reduction performance in DI water owing to the interaction between the microgel particles and the surfactants. Considering that MP is usually used in the laboratory while commercial microgels are provided in the form of ME, the different oil/water interfacial behaviors of MP and ME may result in an inconsistent understanding of the EOR mechanism in laboratory study and field application.

Core- and pore-scale investigation on the migration and plugging of polymer microspheres in a heterogeneous porous media

Polymer microspheres (PMs) can be a very promising, cost-effective in-depth fluid diversion strategy in the development of heterogeneous reservoir. The key to success for the PMs application is to fully understand the PMs-migration and -plugging mechanisms through the confined space. The plugging rate is widely used to evaluate the performance of PMs-plugging. But it always presents a large value using the conventional measurement method even PMs cannot transport through the porous media. The impact factors of PMs-migration and-plugging in previous work based the conventional plugging rate may not be reliable in the reservoir. In this study, three kinds of polymer microspheres (PMs-1, PMs-2, PMs-3) with different particle sizes were synthesized, and their matching relationship with cores and impact factors of plugging were investigated using a new proposed measurement method. Flowing experiment at core- and pore-scale were performed to reveal PMs-migration and -plugging mechanisms. The synthesized PMs had a shape of the regular spheres with initial sizes of 9.8 μm, 6.2 μm and 3.1 μm respectively. They can swell from 3.44 to 2.68 times. The optimal matching factors between PMs sizes and pore sizes were obtained by the redefined plugging strength, which were 1.0–1.2 for PMs-2 and 0.5–0.8 for PMs-3. In the range of the optimal matching factors, PMs-plugging and -migration is affected by PMs sizes rather than the PMs concentration and injection rate. Two plugging patterns of direct-plugging by one single PM and bridge-plugging by multi-PMs were observed in the micromodel. Large PMs was tendency to the direct-plugging, which has much stronger plugging efficiency than the bridge-plugging of multiple small PMs.

The Reservoir Adaptability and Oil Displacement Mechanism of Polymer Microspheres.

Polymer microsphere profile control is a promising approach for the profile control of heterogeneous reservoirs. Matching between polymer microspheres and the reservoir pore throat is crucial for profile control. In this study, the range of the optimal matching factor Ra between polymer microspheres and core porosity was divided through core permeability limit experiments, and the dynamic migration laws and shut-off patterns of microspheres were studied using 9-m-long cores and microscopic models. The oil displacement effect and mechanism of microspheres were analyzed using three cores in parallel. The “injectability limit” and “in-depth migration limit” curves were divided by Ra into three zones: blockage (Ra < 1.09 ± 0.10), near-well profile control (1.09 ± 0.10 < Ra < 5.70 ± 0.64), and in-depth fluid diversion (Ra > 5.70 ± 0.64). During migration in porous media, the microspheres gradually enlarged in size and thus successively shut off in four forms: multi-microsphere bridging shut-off, few-microsphere bridging shut-off, single-microsphere shut-off, and elastic shut-off. Microspheres with a rational combination of sizes versus those with a single particle size further enhanced reservoir oil recovery under certain reservoir conditions. Through “temporary shut-off–breakthrough–temporary shut-off,” the polymer microspheres were able to change the fluid flow rate and streamlines, mobilize residual oils, and enhance the oil recovery rates.

Polymeric microsphere injection in large pore-size porous media

High water-cut has become a worldwide challenge for oil production. It requires extensive efforts to process and dispose. This entails expanding water handling facilities and incurring high power consumption costs. Polymeric microsphere injection is a cost-effective way to deal with excessive water production from subterranean formations. This study reports a laboratory investigation on polymeric microsphere injection in a large volume to identify its in-depth fluid diversion capacity in a porous media with large pore/particle size ratio. The performance of polymeric microsphere injection was evaluated using etched glass micromodels based on the pore network of a natural carbonate rock, which were treated as water-wet or oil-wet micromodels. Waterflooding was conducted to displace oil at reservoir temperature of 95 °C, followed by one pore volume of polymeric microsphere injection. Three polymeric microsphere samples with median particle size of 0.05, 0.3, and 20 μm were used to investigate the impact of particle size of the polymeric microspheres on incremental oil production capacity. Although the polymeric microspheres were much smaller than the pores, additional oil production was observed. The incremental oil production increased with increasing polymeric microsphere concentration and particle size. As a comparison, polymeric microsphere solutions were injected into oil-wet and water-wet micromodels after waterflooding. It was observed that the oil production in oil-wet micromodel was much higher than that in water-wet micromodel. The wettability of micromodels affected the distribution patterns of the remaining oil after waterflooding and further dominated the performance of the microsphere injection. The study supports the applicability of microsphere injection in oil-wet heterogeneous carbonates.

Graft Copolymerization of N-Isopropylacrylamide and Acrylic Acid on Bentonite Colloids for In-Depth Fluid Diversion

A new cost-effective in-depth fluid diversion has been developed and reported. In this paper, the diverting agent is prepared successfully from natural bentonite particles that were modified with N-isopropylacrylamide (NIPAM) and acrylic acid (AA) copolymers. First, bentonite particles were intercalated with small precursor molecules that contained functional groups. These precursors were used to reduce the bentonite particle size and introduce a vinyl group for subsequent polymerization. Then, poly(NIPAM-co-AA) was grafted onto hydrophilic bentonite through a free radical polymerization process. The grafted bentonite morphology, microstructure, and thermal stability were investigated using FTIR spectroscopy, dynamic light scattering, XRD, and TGA measurements. The particle dispersion stability and rheological properties have been investigated by using a turbidimeter and rheometer. Sand packs and core flooding tests were conducted to investigate the injectivity and determine permeability reductions. Exper...

A comprehensive review of polyacrylamide polymer gels for conformance control

Abstract Polymer gels have been designed and successfully applied to improve sweep efficiency and to reduce excessive water production by minimizing reservoir heterogeneity. Based on their compositions and application conditions, polyacrylamide polymer gels can be classified into three types: in-situ monomer-based gel, in-situ polymer-based gels, and preformed particle gels. Initially, in-situ monomer gels which are mainly composed of acrylamide were developed for water shutoff. Conventional in-situ polymer gels include metal-cross linked polyacrylamide gels and organic-cross linked polyacrylamide gels. Preformed gels include preformed particle gels, pH sensitive microgels, and micro- and nano-gels. A few directions are suggested for future research on novel gels, such as gels used for in-depth fluid diversion and gels for severe reservoir environments.

The Application of Performed Particle Gel for Water Shutoff and Flooding in Severe Heterogeneous Reservoir

The success of in-depth fluid diversion and enhancement of the pay zones production are hot issues in long term water flooded oilfields. However, the effect of most chemical-based water cut technologies and conformance-control treatments on fluid profile conformance are normally useful surround near wellbore zones. In addition, chemical particles can probably result in formation damage on low permeable parts of pay zone and the other potential drawbacks. Comparing to general chemical agents such as cross linker, polymer gel, foam fluid and so forth. A water shutoff plugging agent called PPG (Performed Particle Gel) show its advantage in strength-control, size-control and environment-friendly. PPG is a type of gel and synthesized with aqueous, acrylamide, cross linker and the other additives, which can be prepared at surface rather than in the wellbore, thus it is not so sensitive to high temperature and high salinity. A series of studies and field experiments through core flooding were investigated in this paper. The results indicate PPG can significantly achieve in-depth conformance in sever heterogeneous formation and can be widely applied in mature water flooded oil fields. Key words: Heterogeneous; Performed particle gel; Water shutoff; Recovery

The Law of Reservoir Property Change both before and after Water Flooding in Liaohe Oilfield

In order to explore the change laws of physical properties and pore throat radius of reservoir both before and after water flooding to guide the oilfield in-depth fluid diversion, the reservoir properties are analyzed on the basis of core data of early exploratory well and inspection well in the middle and later stages of oilfield development. The theory of reservoir geology and development geology is used to study the change laws of reservoir properties both before and after water flooding in May 20th Development Area of Liaohe oilfield. The research result indicates that reservoir physical properties and pore throat radius have changed in the different period and different microfacies types of sand body [1-3].The permeability is changed far outweigh porosity in the physical properties of reservoir. And with the increase of time, the biggest change is the porosity and permeability of distributary channel, the next are margin of channels, mouth bar. The thin layer of channels and distal bar of physical properties have changed lesser or not. The pore throat radius has declined following distributary channel, mouth bar, thin layer of channels and distal bar in the sedimentary microfacies [4-5].The study results are helpful for the establishment of production measures at the later stage of oilfield development.

Study of Non-Equilibrium Arms Bridge Circuit for Water Plugging of Horizontal Wells in Sandstone Reservoir

In view of rapid water cut increasing and poor oil recovery with banded distribution with high permeability belt in sandstone reservoir of Huabei Oilfield,the electrical bridge technique for water shut-off is proposed. Based on years practice of vertical wells and similarity in Ohms and Darcys laws,the electrical model involved variable resistors series/parallel instead of reservoir distribution,the arm-bridge circuit combined with signal detection. Then response of the circuit by variable water shut-off could be simulated. The results indicated that,the driving pressure and seepage quantity at mid-low permeability channel could be greatly improved by the strong in-depth water-plugging at high permeability channel (L=20~40m),and the low permeability flowrate increased to a maximum of 55.3%. Then the gel dam in-depth fluid diversion technique was verified by water plugging and circuit simulation. The conclusions provided a valuable guidance for horizontal wells development enhanced.

Injecting Large Volumes of Preformed Particle Gel for Water Conformance Control

This paper describes Preformed Particle Gel (PPG) treatments for in-depth fluid diversion in four injection wells located in the northern section of the Lamadian reservoir, Daqing oilfield, China, which is a sandstone reservoir with thick heterogeneous pay zones. Forty-six producers were connected to the four treated injectors with an average water cut of 95.4% before PPG treatments. A large volume (more than 1 000 m<sup>3<sup/>) of PPG suspension with concentrations of 1900-2 500 mg/L and particle sizes of 0.06-3.0 mm was injected into each well, each injection spanning approximately four months. The injection PPG suspension volumes range from 11458 to 17625 m<sup>3<sup/> per well with a total of 56269 m<sup>3<sup/> (295680 lb of dried PPG) for the four wells, which indicated the existence of super-K zones or fractures in the formation. During PPG injection, real-time data, including injection pressure, injection rate and particle sizes, were monitored to tune our treatment design and to analyze the practical status of the mature reservoir. This paper reports detailed information for the four well treatments, including well candidate selection criteria, treatment design, real-time monitoring results during PPG injection and treatment results.

Mechanism research of in-depth fluid diversion by “gel dam” place with horizontal well using X-ray CT

Abstract According to the concept of in-depth fluid diversion by “gel dam” place with horizontal well, its EOR mechanism is studied by means of laboratory water flooding experiment combined with X-ray computer tomography (CT) technique. In the experiment, the artificial cementing heterogeneous model is casted with epoxy resin on surface, and the flooding processes before and after the “gel dam” formed are scanned dynamically by X-ray CT. Through observing the distribution feature of gel dam, tracking the oil and water distribution, water flooding streamline change, oil saturation distribution and its dynamic variation, it is indicated that “gel dam” can effectively shut off the deep channeling in higher permeability layer, and divert the injected water into upper low-permeability layer to displace the remaining oil therein. After “gel dam” is formed, the ultimate oil recovery by water flooding increased by 16.7%, and the water cut ascending velocity slowed down. With “gel dam” technique, gel can be placed in the in-depth reservoir zone to achieve in-depth fluid diversion, which increase the water flooding sweep efficiency and oil recovery. “gel dam” in-deep fluid diversion technique is a promising EOR method for positive rhythm thick reservoirs.

Physical modeling of in-depth fluid diversion by “gel dam” placed with a horizontal well

Ineffective cycling of injected water in high permeability zones during water flooding processes can be an issue in positive rhythm reservoirs. The “gel dam” in-depth fluid diversion technique is proposed to ameliorate this problem. The technique involves the injection of gel by horizontal wells drilled in the highly permeable and strongly swept zones of thick positive rhythm reservoirs. The injected water then will bypass the “gel dam” and be diverted into the upper, lower permeability zones. As a result, the sweep efficiency and oil recovery from the overlying low permeability zone can both be increased. A 2D visible sand-pack physical model was set up to test the process, and a video camera was used to visualize the “gel dam” fluid diversion effects. The results of the experiments indicated that, with one or two “gel dams”, both the sweep volume and ultimate oil recovery increased greatly, while the rate of water cut decreased. Compared with physical models with no “gel dam”, the ultimate oil recoveries of those with one or two “gel dams” increased by 17.6% and 27.3%, respectively. By applying the “gel dam” in-depth fluid diversion technique, difficulties in the in-depth placement of plugging agents can be resolved, and the sweep efficiency of positive rhythm reservoir can be increased significantly.

Applied Technologies and Prospects of Conformance Control Treatments in China

China is the largest user of chemical-based conformance control treatments and a series of technologies have been successfully developed and deployed in recent years. This paper first shows the milestones of development and application of conformance control technologies in China. Then integrated conformance control technologies are reviewed followed by the lessons we have learned, and then a few major specific conformance control technologies are addressed, including tracer injection and channels explanation, potentiometric testing to identify areal sweep efficiency, Pressure Index (PI) decisionmaking technology to select well candidate, complementary decision-making technology to select well candidate and design application parameters, and major chemicals for in-depth fluid diversion technologies. In addition, this paper also describes the principles and applications of some promising technologies of combined chemical-based conformance treatment with other EOR/IOR process, including the combination technology of surfactant and water shutoff, profile control and mini-scale surfactant flooding, acid treatment and profile control treatment. Finally, this paper summarizes the problems and challenges faced by mature water flooded oilfields in China. Based on recent well tests, tracer testing and interpretation, and previous water control treatment experience, it appears that channels or high permeability streaks are common in mature water flooded oilfields. Some research directions and promising technologies are suggested.

The Application of Oily Sludge in Chinese Oilfield

Using industry wastes for conformance control has recently attracted significant interest—in particular, when using oily sludge for in-depth fluid diversion. About 500 tons of oily sludge is generated from oil production, transportation, and refining each year. Oily sludge is mainly composed of oil, water, o/w emulsions, and solids and is quite difficult to separate and reuse. The accumulation of oily sludge has posed a serious environmental problem. Additives such as suspension agents, dispersion agents, and viscosity thickeners are often added into oil sludge as conformance control agents to extend particle suspension time, increase plugging efficiency, disperse oily drop, and increase penetration depth. The advantages of oily sludge as conformance control agents include: (1) good compatibility with formation; (2) high temperature resistance; (3) high salinity resistance; (4) low costs; and (5) environmental protections. This method has been used by most oilfields in China, with better results.

Method of analysis of porous structure of sintered porous materials : N.Y.Crjuchkov. Poroskovaya Metall., no 5/6, 1996, 64–70. (In Russian.)

Polymer gels have been designed and successfully applied to improve sweep efficiency and to reduce excessive water production by minimizing reservoir heterogeneity. Based on their compositions and application conditions, polyacrylamide polymer gels can be classified into three types: in-situ monomer-based gel, in-situ polymer-based gels, and preformed particle gels. Initially, in-situ monomer gels which are mainly composed of acrylamide were developed for water shutoff. Conventional in-situ polymer gels include metal-cross linked polyacrylamide gels and organic-cross linked polyacrylamide gels. Preformed gels include preformed particle gels, pH sensitive microgels, and micro- and nano-gels. A few directions are suggested for future research on novel gels, such as gels used for in-depth fluid diversion and gels for severe reservoir environments.