Bisweswar Ghosh

The Application of Direct Current Potential to Enhancing Waterflood Recovery Efficiency

Abstract Advantages of direct current (DC) application, concurrently with waterflooding, in mobilizing trapped oil is investigated. Application of DC on completely water swept core recovered 3–9% additional oil, which is slightly less when DC is applied from the beginning of waterflooding process. Reduced water requirement (15–22%) and permeability enhancement up to 40% are found to be added benefits. The effect is more pronounced in higher permeability core and higher density oil. These phenomena are attributed to formation of clay colloids and mobilization of trapped oil along with connate water due to the added dynamics of electrokinetic and electrochemical processes.

Field Application of Phenol Formaldehyde Gel in Oil Reservoir Matrix for Water Shut-off Purposes

Abstract A few wells from a major western India on-shore oil field are either on the verge of being shut in or have already been abandoned due to excessive water-cut (WCT) levels. Low injectivity and extreme temperatures (149°C) make it difficult for water shut-off by conventional polymer gel injection. A water-thin monomer-based in situ gelation system has been developed and successfully tried in one of the wells that ceased production due to 100% WCT. The average production of 420 barrel of oil per day (BOPD) with less than 1% WCT, in the first year of production back in 1996, has declined to less than 8 BOPD (with 98% WCT) prior to shut-in in year 2002. A rise in the oil-water contact level in combination with a coning effect was diagnosed as a possible cause of the high WCT, which was later controlled by a newly developed gelant treatment. In fact, the average post-treatment production for the first 3 months was nearly 200 BOPD. Thereafter, production gradually stabilized in the neighborhood of 115 BOPD with a WCT of 48%. Cheap chemicals and a fast treatment method have resulted in a payback time span of 5 days and made an additional profit of U.S.

The Stimulation of Sandstone Reservoirs Using DC Potential

0.6 M. The water shut-off job resulted in an impressive commercial success; technical success, however, was less than satisfactory due to the fact that, in spite of using a water-thin monomeric solution, only 40% of the designed volume could be injected due to low injectivity resulting in an abnormal pressure build-up. In addition to the gel development and treatment experiences, this article describes in detail the results of further lab investigations carried out to identify the possible reasons causing injection failure.

The Effect of DC Electrical Potential on Enhancing Sandstone Reservoir Permeability and Oil Recovery

Abstract The authors describe the effect of direct current application in conjunction with waterflood on improving flow properties of Berea sandstone cores. Single- and two-phase flow experiments are conducted on a specially designed coreflood setup, under constant electrode potential. The results showed that core permeability may increase up to 223% when hydraulic gradient and electroosmotic flow are applied in the same direction. The effect is insignificant when they work in opposite direction. It is verified from experimental results that dislodgement of clay in colloidal form, resulting increase of effective pore throat diameter improved hydraulic permeability.

A Novel Method for Improving Water Injectivity in Tight Sandstone Reservoirs

Abstract The merits of using electrokinetic phenomena to improve reservoir permeability on sandstone reservoir core plugs are investigated with detail clay mineralogy studies. Normal and reverse DC configuration is applied along with waterflood and studies are conducted on single-phase and two-phase fluid saturation conditions. The produced brines are acid digested and analyzed by inductively coupled plasma mass spectroscopy (ICP-MS). In single-phase flow experiments, permeability enhanced 180% with the normal electrode configuration but negligible change is observed in reverse configuration. In two-phase flow 59% and 10% permeability enhancement is observed in normal and reverse configurations, respectively. In addition, 11.6% additional oil is recovered from normal configuration. The results are examined in terms of electrolyte movement and resulting changes within the clay microstructure. In normal electrode configuration, formation of colloidal clay suspension and flowing out along with produced brine is evident. This has resulted in increased pore passage and core permeability, whereas in the reverse configuration, clay structures remained unchanged. The given explanations are supported by ICP-MS and X-ray diffraction results.

A Review on the Progress of Ion-Engineered Water Flooding

Applicability of electrokinetic effect in improving water injectivity in tight sandstone is studied. DC potential and injection rate are varied for optimization and determination of their individual impact on clay discharge and movement. The liberated clays were characterized through size exclusion microfiltration and ICP-MS analysis. Real time temperature and pH monitoring were also informative. Results showed that severalfold (up to 152%) apparent increase of core permeability could be achieved. Some of the experiments were more efficient in terms of dislodgement of clays and enhanced stimulation which is supported by produced brines analysis with higher concentration of clay element. The results also showed larger quantity of clays in the produced brine in the initial periods of water injection followed by stabilization of differential pressure and electrical current, implying that the stimulation effect stops when the higher voltage gradient and flow rates are no more able to dislodge remaining clays. Additionally, fluid temperature measurement showed an increasing trend with the injection time and direct proportionality with the applied voltage. The basic theory behind this stimulation effect is predicted to be the colloidal movement of pore lining clays that results in widening of pore throats and/or opening new flow paths.

Development of a New Copolymer for Oil Field Carbonate Scale Mitigation

In the oil and gas industry, Enhanced Oil Recovery (EOR) plays a major role to meet the global requirement for energy. Many types of EOR are being applied depending on the formations, fluid types, and the condition of the field. One of the latest and promising EOR techniques is application of ion-engineered water, also known as low salinity or smart water flooding. This EOR technique has been studied by researchers for different types of rocks. The mechanisms behind ion-engineered water flooding have not been confirmed yet, but there are many proposed mechanisms. Most of the authors believe that the main mechanism behind smart water flooding is the wettability alteration. However, other proposed mechanisms are interfacial tension (IFT) reduction between oil and injected brine, rock dissolution, and electrical double layer expansion. Theoretically, all the mechanisms have an effect on the oil recovery. There are some evidences of success of smart water injection on the field scale. Chemical reactions that happen with injection of smart water are different in sandstone and carbonate reservoirs. It is important to understand how these mechanisms work. In this review paper, the possible mechanisms behind smart water injection into the carbonate reservoir with brief history are discussed.

Flow visualization of fingering phenomenon and its impact on waterflood oil recovery

Abstract Calcite scale deposition along the flow path is the most common among flow assurance problems in oil wells. Frequent well cleaning creates a major increase in operating cost. In order to minimize the formation of scale deposits, threshold scale inhibitor treatment is a common practice in oil industry. The authors describe synthesis, characterization, and comparative evaluation of a low molecular weight maleic acid-methacrylic acid copolymer as potential calcite scale inhibitor. GPC and FT-IR were employed for molecular characterization; scale inhibition efficiency was studied through a static jar test, a dynamic tube block method, and also through an electrochemical technique (e.g., electrochemical impedance technique). SEM analysis demonstrated inhibited and uninhibited crystal morphology, and 100% scale inhibition was possible at a low dose of 20–25 ppm throughout the test regime.

Tight Reservoir Stimulation for Improved Water Injection - A Novel Technique

Oil recovery prediction and field pilot implementations require basic understanding and estimation of displacement efficiency at the microscopic level. Glass micromodels are commonly used to determine microscopic sweep efficiency and to visualize the flow behavior. In this paper, we investigate the fingering phenomena during immiscible displacements as well as the relationship between capillary number, oil recovery, and wave characteristics of developed fingers. An etched glass micromodel with three layers of large permeability contrasts was used in this work. The fluids used include a filtered deionized water and two field oil samples. Waterflood recovery to residual oil saturation was measured through image tool analysis techniques. The results showed that the low-permeability layer resulted in higher displacement efficiency compared to the medium- and high-permeability layers. At the microscopic level, fingering phenomena are attributed for the latter finding. An early occurrence and growth of multiple fingers were observed for high-permeable layers, whereas finger growth was delayed in layers with low permeability. Peter and Flock equation was used to draw a relation between oil recovery and finger characteristics, where the increase in capillary numbers leads to a decrease in both instability scaling index and incremental oil recovery. Moreover, the limitations of Peter and Flock equation were also highlighted for strongly water-wet systems. This paper helps field operators to gain more insight into microheterogeneity and fingering phenomena and their impact on waterflood recovery estimation.

A New Squeeze Scale Inhibitor for a Sandstone Reservoir with a Stimulation Effect

Among the emerging technologies in the petroleum industry is the application of electro-kinetic phenomena to enhance oil recovery from tight heavy sandstone reservoir, which has been reported to yield technical and commercial success in some of the North American oil fields. The basic theory behind the stimulation effect is predicted to be the colloidal movement of pore lining clays that results in widening of pore throats and/or opening new flow tunnels. Nevertheless, few works have been performed on its applicability to water injection wells. This paper investigates the effect of electrokinetics on improving water injectivity in tight sandstone reservoirs. Two sets of experiments were conducted. In the first set, the DC potential is varied and optimized during the water injection. In the second set, the DC potential is kept constant and the injection rate is varied to determine the hydrodynamic effect on clay movement. The core plugs and liberated clays were characterized through size exclusion micro-filtration and ICP-MS analysis. The Joule heating phenomena associated with electrokinetics is also studied during the entire injection period. Results showed that several folds (up to 152%) apparent increase of core permeability could be achieved. Some of the experiments were more efficient in terms of dislodgement of clays and enhanced stimulation which is supported by produced brines analysis with higher concentration of clay elements. The results also showed larger quantity of clay elements in the produced brines in the initial periods of water injection, prior to the stabilization of differential pressure and electrical current, implying that the stimulation effect stops when the voltage gradient and flow rate values are no more able to remove additional clays. Additionally, fluid flow temperature measurements showed an increasing trend with the injection time and direct proportionality with applied voltages.