Reducing uncertainty at the Chichimene in situ combustion pilot by means of a nitrogen connectivity test

Abstract

Prior to start any Enhanced Oil Recovery (EOR) process, it is desirable to characterize the flow pattern within the affected reservoir volume. This becomes of critical importance for in situ combustion in heavy oil reservoirs, where the mobility ratio is highly unfavorable, oftentimes resulting in channeling or early breakthrough. An inter-well connectivity test through immiscible gas injection aids improving the characterization of the flow distribution, in addition to: 1) calibrating estimates for sweep efficiency; 2) evidencing geological features that may lead to preferential flow towards a particular well or group of them, or lack of connection amongst them; 3) creating a gas path between the injector and producer wells to enable a safe progression of the combustion front; and 4) evaluating the performance of artificial lift and well control systems under high gas-liquid ratio conditions. A connectivity test using nitrogen was designed, implemented and evaluated at the Chichimene field, prior to the ignition of the in situ combustion pilot. This process is summarized and described in this paper. This will be the first in situ combustion trial in a deep (≈ 8000 ft.), extra-heavy oil reservoir, and will serve as a data source to evaluate the development of resources under similar conditions in the eastern plains basin of Colombia. This set of reservoirs bears a significant fraction of the hydrocarbon resources in the country and under Ecopetrol operation. The importance of this pilot makes this connectivity test of even larger relevance to reduce the subsurface and operational uncertainty, identifying potential risks, and increase the probability of success of the combustion process as an option to economically produce these resources.