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.