In-depth Profile Modification Research Articles

Laboratory evaluation and numerical simulation study on profile modification performance of gel-nitrogen-foam for low permeability formation under fracturing

In-depth water flooding profile modification is a new problem for low permeability formation under fracturing. Profile control study for in-depth cross flow which couples fracture and matrix is neither comprehensive nor complete at present. Artificial hydraulic fracturing core is manufactured to conduct core flood experiment. In-depth profile modification mechanisms of gel-nitrogen-foam are revealed based on microstructure analysis and mechanical stability evaluation. The instantaneous stability and durability of gel-nitrogen-foam are evaluated by breakthrough pressure and residual resistance factor. Weak movement ability restrains the distribution of gel in cross zone and bubble burst effect declines the active time of nitrogen-foam. Gel-nitrogen-foam displays promised profile modification performance based on synergistic effect which combines movement ability of nitrogen-foam and durability of gel. Nuclear magnetic resonance (NMR) test result shows that sweep area of matrix significant increases after profile modification, which indicates that enhance oil recovery (EOR) main contributes by the remaining oil in matrix nearby injection fracture. The optimized gas/liquid ratio and injection volume are 1.95 and 2.8 PV separately with incremental EOR of 9.74%. Coupling laboratory experiment with numerical simulation, this work offers a new insight of in-depth cross flow profile modification mechanism for formation under fracturing from macroscopic and microscopic views.

Investigation of inverse emulsion assisted controlled release of polyacrylamides for enhanced oil recovery.

Conventional polymer flooding (e.g. using polyacrylamide) has been widely used in the oil fields as an economical means for enhanced oil recovery. However, its efficacy is affected by the polymer properties and increasingly harsh reservoir conditions. In this study, a high-molecular-weight modified polyacrylamide polymer (GF-1) encapsulated in a water-in-oil emulsion is proposed for controlled polymer release towards enhanced oil recovery. It is compared with the conventional polyacrylamide in terms of their microscopic morphology, dissolving capacity, concentration–viscosity relationship, and rheological properties. It contained swollen polymer micelles and gradually released the polymer after phase inversion, which caused its viscosity, viscoelasticity, and plugging capacity to increase with aging time. The plugging analysis surprisingly showed a four-fold increase in the dimensionless breakthrough pressure of the emulsion polymer and five-fold increase in the residual resistance factor after five days of aging, confirming the significant increase in viscosity in confined spaces. The most interesting results were obtained by parallel core flooding experiments, where a higher recovery factor of 2.7% more than the conventional polymer was observed for GF-1 and GF-1 outperformed the conventional polymer by 6.9% in the low permeability zone. This emulsion polymer is a promising material to achieve enhanced oil recovery using in-depth profile modification in future oilfield related efforts.

貯留層内ブロッキングによる掃攻率改善効果の検討

貯留層内ブロッキングによる掃攻率改善効果の検討

芦田ら著論説「不均質性を考慮した掃攻率改善のための効果的貯留層内ブロッキングの検討」に対する質問

芦田ら著論説「不均質性を考慮した掃攻率改善のための効果的貯留層内ブロッキングの検討」に対する質問

「不均質性を考慮した掃攻率改善のための効果的貯留層内ブロッキングの検討」に対する質問への回答

「不均質性を考慮した掃攻率改善のための効果的貯留層内ブロッキングの検討」に対する質問への回答

A Comparison of Polymer Flooding With In-Depth Profile Modification

Summary For stratified reservoirs with free crossflow and where fractures do not cause severe channeling, improved sweep is often needed after water breakthrough. For moderately viscous oils, polymer flooding is an option for this type of reservoir. However, in recent years, an in-depth profile-modification method has been commercialized in which a block is placed in the high-permeability zone(s). This sophisticated idea requires that (1) the blocking agent have a low viscosity (ideally a unit-mobility displacement) during placement, that (2) the rear of the blocking-agent bank in the high-permeability zone(s) outrun the front of the blocking-agent bank in adjacent less-permeable zones, and that (3) an effective block to flow form at the appropriate location in the high-permeability zone(s). Achieving these objectives is challenging but has been accomplished in at least one field test. This paper investigates when this in-depth profile-modification process is a superior choice over conventional polymer flooding. Using simulation and analytical studies, we examined oil-recovery efficiency for the two processes as a function of (1) permeability contrast, (2) relative zone thickness, (3) oil viscosity, (4) polymer-solution viscosity, (5) polymer- or blocking-agent-bank size, and (6) relative costs for polymer vs. blocking agent. The results reveal that in-depth profile modification is most appropriate for high permeability contrasts (e.g., 10:1), high thickness ratios (e.g., less-permeable zones being 10 times thicker than high-permeability zones), and relatively low oil viscosities. Because of the high cost of the blocking agent relative to conventional polymers, economics favors small blocking-agent-bank sizes (e.g., 5% of the pore volume in the high-permeability layer). Even though short-term economics may favor in-depth profile modification, ultimate recovery may be considerably less than from a traditional polymer flood.

不均質性を考慮した掃攻率改善のための効果的貯留層内ブロッキングの検討

Most of the conventional EOR processes have already been established, and the development of a new innovative EOR process is quite difficult. Therefore, the sweep efficiency improvement (SEI) is more important for an efficient EOR. Several SEI methods have been applied actually in many fields. However, the injected EOR fluid tends to flow selectively in the already swept high permeable zones, and the sweep efficiency is poor as the result. In this case, in-depth profile modification by blocking such the already swept high permeable zones with a polymer gel would be a more effective than already existing SEI methods.In this study, numerical simulations to confirm the effect of the in-depth profile modification on SEI has been conducted to thirty-two heterogeneous reservoir models under the several blocking conditions. The relation between the blocking effect on SEI and the heterogeneity indexes, which are Dykstra-Parsons coefficient for vertical heterogeneity and correlation length for horizontal heterogeneity, is also investigated.From this study, following results have been obtained. First, the blocking effect increases with the increase in the volume of injected polymer gel and the decrease in the volume of chase water. That is to say, the blocking effect increases when the blocking is done more perfectly. Second, the blocking effect increases with the increase in the vertical heterogeneity, and horizontal heterogeneity is less correlated to the blocking effect compared to the vertical heterogeneity.

Evaluation of modified cationic starch for impeding polymer channeling and in-depth profile control after polymer flooding

Premature polymer production in large quantities from flooding reservoirs is a serious problem commonly existing in some large oilfields in China. This is owing to polymer channeling through high permeability zones or pore passage. This paper presents a novel modified cationic starch, which can react with partially hydrolyzed polyacrylamide (HPAM) remaining in reservoir formation to form gels in-situ. The obtained gels can reduce polymer channeling and make successive injected water into mid-low permeability zones that achieve the purpose of deep profile control. The rheological property and the gel strength are examined. The singular sand-pack core-flood test results provide experimental evidence that the formed gel system is more effective in plugging high permeability pore passages. Moreover, the parallel core-flood test was conducted to simulate the process of in-depth profile modification in a heterogeneous formation. It has been found that this gel system can significantly enhance oil recovery and effectively reduce water-cut.

Molecular Configuration and Flow Performance of Al3+ Cross-linked Polymer

According to the difference in compositions of Al3+ cross-linked polyacrylamide gel, there are two types of cross-linked reactions. One is the intramolecular cross-linked reaction that takes place in different chains of the same polymer molecule, and the other is the intermolecular cross-linked reaction, which takes place among different polymer molecules. Through changing the compositions of the cross-linked polymer and gelling environment, thorough research on the critical conditions and flow performance of intramolecular cross-linked polymer is carried out. The results show that the viscosity of the intramolecular cross-linked polymer almost remains the same over time, but during the flow performance experiments, the resistance factor and residual resistance factor are higher, and the residual resistance factor is larger than the resistance factor. The higher the salinity of solvent, the easier the intramolecular cross-linked polymer forms. In the scope of concentration of cross-linking agent, the higher the concentration of cross-linking agent, the easier the intramolecular cross-linked polymer forms. The higher the temperature, the easier the intramolecular cross-linked polymer forms. For the minerals that influence the molecular configuration of cross-linked polymer, the influence of Ca2+ is the biggest, then Mg2+, the least being Na+. A pilot test in the Pu I1-4 reservoir of the Daqing oilfield showed that the in-depth profile modification using intermolecular cross-linked polymer solution has characteristics of lower cost and easier injection technique, and can gradually form gel through the process of injection. When the effect of gel forming is at its best state, the injection pressure can reach the highest and retain relatively stable values. Therefore, comprehensive watercut would decrease and oil production rate would increase, which can be used as an important whole profile modification technique.

Effects of shear fracture on in-depth profile modification of weak gels

Two sand packs were filled with fine glass beads and quartz sand respectively. The characteristics of crosslinked polymer flowing through the sand packs as well as the influence of shear fracture of porous media on the indepth profile modification of the weak gel generated from the crosslinked polymer were investigated. The results indicated that under the dynamic condition crosslinking reaction happened in both sand packs, and the weak gels in these two cases became small gel particles after water flooding. The differences were: the dynamic gelation time in the quartz sand pack was longer than that in the glass bead pack. Residual resistance factor (FRR) caused by the weak gel in the quartz sand pack was smaller that that in the glass bead pack. The weak gel became gel particles after being scoured by subsequent flood water. A weak gel with uniform apparent viscosity and sealing characteristics was generated in every part of the glass bead pack, which could not only move deeply into the sand pack but also seal the high capacity channels again when it reached the deep part. The weak gel performed in-depth profile modification in the glass bead pack, while in the quartz sand pack, the weak gel was concentrated with 100cm from the entrance of the sand pack. When propelled by the subsequent flood water, the weak gel could move towards the deep part of the sand pack but then became tiny gel particles and could not effectively seal the high capacity channels there. The in-depth profile modification of the weak gel was very weak in the quartz sand pack. It was the shear fracture of porous media that mainly affected the properties and weakened the in-depth profile modification of the weak gel.

Applications of Weak Gel for In-Depth Profile Modification and Oil Displacement

Abstract Water breakthrough is a common problem when an oil field is waterflooded. Polymer solutions are widely applied to resolve the water channeling problem in deep formations. In practice, polymers are used in deep formation treatments either to block in-depth high permeability zones or to improve the mobility ratio. However, the major challenge for in-depth profile modification is how to deliver the gelling solution to the target zones. To this end, a polymer solution has to be injected at a high concentration. Thus, such a treatment sometimes becomes uneconomical. On the other hand, polymer flooding is ineffective primarily due to the viscosity loss caused by mechanical and chemical degradation. In this paper, a weak gel system is developed and used as an in-depth profile modification agent and as an oil displacement agent in a heterogeneous reservoir. The gel system has relatively low strength but can still be crosslinked in the reservoir formation. In comparison with a pure polymer solution, it suffers from less mechanical and chemical degradation because of its crosslink reaction. The EOR mechanisms of the weak gel system are described briefly. The detailed effects of polymer concentration, crosslinker concentration, temperature, and pH on gelation time are studied. Also the rheological properties, gelation range, and gel strength are examined. The coreflood results provide experimental evidence that the weak gel acts both as an in-depth profile modification agent and as an oil displacement agent. Furthermore, pilot tests have been performed in the Gudong and the Gudao oil fields of the Shengli oil field in China since 1992. The cummulative incremental oil production has been over 58,000 tonnes at the end of 2001. Introduction Waterflooding is the most widely used technology for improving oil recovery. However, early water breakthrough is a common problem encountered in almost every waterflooded oil field. Severe water channeling can result in low waterflooding efficiency and sometimes even make waterflooding uneconomical. There are several reasons for water breakthrough. Sometimes, it happens near the wellbore region, such as breakthrough along the casing due to poor cementing quality. In other cases, water breakthrough occurs in a deep formation because of its heterogeneity or fractures. In addition, because of the mobility difference between the displacing phase and the displaced phase, the former tends to bypass the latter in a homogeneous formation. In this case, viscous fingering is inevitable and early water breakthrough occurs in the producers(1–3). Different technologies have been implemented to reduce the high water-cut caused by water breakthrough, among which the most widely used is polymer injection. In general, polymer is increasingly used in chemical EOR in two traditional ways: either as an in-depth profile modification agent in conformance control, or as an oil displacement agent in polymer flooding. For conformance control, polymer and crosslinker are injected into formations to reduce large channeling through fractures or high permeability zones without damaging the productivity of the hydrocarbon. However, due to the prompt crosslink reaction, gel is sometimes formed near the wellbore.

Application of a Novel Polymer System in Chemical Enhanced Oil Recovery (EOR)

Water breakthrough is a common technical problem during the course of water flooding in an oil field. Polymer solution is widely applied to resolve the water-channeling problem in a deep formation. In practice, polymer is used in deep formation treatment either to form a gel blockage and plug high permeability zones in situ, or to act as a mobility control agent and increase the viscosity of injected fluids. However, for an in-depth profile modification operation, a polymer solution has to be injected at a relatively high concentration so as to maximize its penetration. Thus such a treatment may be uneconomical. On the other hand, a traditional polymer flooding may become ineffective mainly due to the viscosity loss caused by mechanical and chemical degradations. This paper presents a novel polymer solution, which is classified as a weak gel system and can be used in chemical enhanced oil recovery (EOR) as an in-depth profile modification agent, and as an oil displacement agent simultaneously in a heterogeneous reservoir. The weak gel system has relatively low strength but can still be cross-linked in the reservoir formation. In comparison with a conventional conformance control agent, this weak gel can form a blockage in a deeper formation due to its mobile feature. The EOR mechanisms of the weak gel system are described in detail. In addition to the effects of temperature, concentration, and pH value on gelation time, the rheological property, gelation range, and gel strength are examined. The core-flood test results not only provide experimental evidence that the weak gel improves injection profile and increases sweep efficiency but also show enhanced oil recovery. Furthermore, the pilot tests have been performed in Gudong and Gudao oil fields in China since 1992. It has been found that this weak gel system can significantly enhance oil recovery and effectively reduce water-cut. By the end of 2001, the cumulative incremental oil production had been over 58 000 tons.