Das, Alolika (The University of Texas at Austin) | Nguyen, Nhut (The University of Texas at Austin) | Alkindi, Abdullah (PDO) | Farajzadeh, Rouhi (Shell Technology Oman) | Azri, Nasser (PDO) | Southwick, Jeffrey (Shell Global Solutions Intl. B.V.) | Vincent-Bonnieu, Sebastien (Shell Global Solutions Intl. B.V.) | Nguyen, Quoc P. (The University of Texas at Austin)
Chemical enhanced oil recovery (EOR) in carbonate reservoirs has always been technically and economically challenging. Conventional Alkaline-Surfactant-Polymer (ASP) flooding has limited application in low permeability (2-20 mD) and high salinity formations (~200,000 ppm TDS) with a large concentration of divalent cations. Also injectivity into such low permeability reservoirs can be a significant problem with polymer solutions.
The process of low tension gas (LTG) in tight carbonates has exhibited good microscopic displacement and mobility control. It combines interfacial tension (IFT) reduction with improved mobility control by in-situ generation of foam in low-permeable heterogeneous formations. This process has been tested in the lab for a Middle Eastern carbonate reservoir, which is the subject of this paper. This strategy has been tested through either co-injection or alternating injection of slug/drive surfactant solution and gas (CO2, N2, or hydrocarbon) at low foam quality (high water content). A successful surfactant screening was performed to select the optimum surfactant formula that exhibits ultra-low IFT, good aqueous stability, and low microemulsion viscosity. The formulation allows tailoring of optimal salinity for ultra-low oil-water IFT to the variation of formation and produced water salinity. Core flood experiments have been performed, which demonstrated favorable mobilization and displacement of residual oil. Tertiary recoveries of up to 85% on remaining oil were achieved for cores with permeability less than 10 mD. An innovative experimental method was also developed to achieve high initial oil saturation in tight rocks.
Polymer flooding is the most commonly applied chemical enhanced-oil-recovery technique. This paper provides an update on the status of polymer-flooding technology, focusing more on field applications than on theoretical and laboratory research. It covers the following topics: • Mechanisms of polymer flooding • Polymers used • Polymer-solution stability • Technical screening criteria • Laboratory and simulation work • Performance-monitoring technique • Summary of pilots and large-scale applications • Experience and learning from field projects • Polymer flooding in heavy-oil reservoirs • Polymer viscoelastic properties • Problems associated with polymer flooding and their solutions • Future developments The data and analysis presented in this paper will give readers updated information describing polymer flooding, as well as a guide to the relevant research. Survey data will also provide operators with reference data for project design and optimization.
Al-Rashdi, Yaqoob Salem (Petroleum Development Oman LLC) | AL Kindi, Abdullah (Petroleum Development Oman LLC) | AL Bulushi, Sameer (Petroleum Development Oman LLC) | Azri, Nasser (Petroleum Development Oman LLC) | Te Riele, Paul M (Shell Technology Oman)
Heavy oil fields with complex geology present a great challenge for a commercial development. The field described in the paper is a heterogeneous, sparsely fractured carbonate field with oil viscosity of 5,000 –10,000 cP. Initial production test proved that the field cannot be commercially developed using conventional development primary and secondary recovery technologies.
A number of EOR recovery processes have been reviewed for applicability to this field. A fit for purpose uncertainty analysis on key parameters lead to the conclusion that thermal recovery methods are not technically feasible mainly due to steam confimenent issues. A solvent based EOR development scheme was identified as a potential recovery route for such reservoir environment. A feasibility study was conducted to determine whether solvent injection is attractive under a number of realistic subsurface realizations and completion strategies. This study resulted in a number of activities to derisk uncertainties and come to quality decisions towards a solvent development.
Series of field tests have been conducted to mitigate some of the risks associated with the solvent development. Firstly, given the low permeability and low oil mobility, the presence of mobile water is essential in order to inject the solvent and contact the oil with the solvent. Water injection tests were carried out to demonstrate the presence of mobile water in all different reservoir zones and confirmed matrix injectivity is possible. A next step is to utilize the mobile water to inject a solvent into the reservoir and contact the oil accordingly for which a solvent test is planned using a mixture of xylene and diesel. A xylene-diesel mixture was selected as this showed in laboratory tests first contact miscibile with the field crude oil and is readily available for field application. The objectives of this single well injection test are to 1) confirm and quantify solvent injectivity, 2) prove heavy oil mobilization through solvent EOR methods from carbonate reservoir settings and 3) to determine near wellbore sweep efficiency of solvents injected into long horizontal wells. If successful a multi well continuous injection trial will be designed and executed.
This paper describes the design and analysis of the single well solvent injection test for this heavy oil carbonate field. It also describes the experimental lab work conducted to confirm xylene-diesel compatibility with the field crude oil and its suitability for application in a solvent EOR development derisking.
This paper describes key aspects related to conceptual well completion design and surveillance planning for an evolving polymer field trial in the South of Oman. An existing field was developed with mostly horizontal production wells drilled at the top of the oil column to deliver high oil production rates. The production of this medium-heavy oil is supported by a strong bottom drive. However, many wells have observed premature water breakthrough resulting in high water cuts and large volume of unswept oil. Polymer flooding using a horizontal well approach is proposed to improve sweep efficiency. If successful, this alternative approach has the potential to significantly improve oil recovery in the subject field.
Because of the significant investment required and novelty of the process (i.e. heavy oil, strong bottom water drive combined with the use of horizontal wells), a field trial is planned to address some of the development risks. Key subsurface risks and uncertainties include: possible polymer losses to the underlying aquifer, loss of effective matrix polymer injectivity, lack of polymer injection conformance along the horizontals and poor sweep efficiency. A number of activities were performed to help design the field trial and reduce some key risks and uncertainties i.e. laboratory coreflood, subsurface study, injectivity test and field visit to analogue field.
The study concluded horizontal polymer injectors placed between the existing producers and slightly deeper than the centre of the oil column is optimum to recover the unswept oil. Polymer injector with Smart completion is proposed to mitigate the lack of conformance along the horizontals. A detailed surveillance plan is critical to identify the required tools and technologies to facilitate data gathering and well intervention activities during the field trial. Proposed surveillance technologies are DTS, Multi Pressure Sensors (MPS) and saturation logging. Observation wells with glass reinforced epoxy (GRE) pipe are planned to get a higher accuracy and deeper investigation of the formation saturation. These activities will be supported by calibrated subsurface simulation models as new data is available to address the trial performance, as well as, better predict full-field performance.
Brooks, David (Shell Intl. E&P Co.) | De Zwart, Albert Hendrik (Shell Intl. E&P Co.) | Bychkov, Andrey (Shell) | Azri, Nasser (Shell International EP) | Hern, Carolinne (Shell) | Al Ajmi, Widad (Petroleum Development Oman) | Mukmin, Mukmin (Petroleum Development Oman)