Conversion of Cyclic Steam Injection to Continous Steam Injection

Abstract

Abstract Estimated total world in-place oil volumes are between 9 trillion and 13 trillion barrels, of which 30% is conventional crude. The rest is 30% oil sands and bitumen, 25% is "extra heavy" oil and 15% is "heavy" oil. Normally definition of heavy oil is based on gas free properties of the oil. An oil is classified as heavy oil if the dead oil viscosities are between 100 centipoises to 10000 cp at reservoir temperatures with API's between 10 to 20. Extra-heavy oil is commonly defined as oil having a gravity of less than 10° and a reservoir viscosity more than 10 000 centipoises. When reservoir viscosity measurements are not available, extra-heavy oil is considered to have a lower limit of 4° API (WPC Report - 2007). Though industry has known about heavy oils for a century, it still provides a minute fraction of the world's production. Because in many cases oil will not flow at economical rates (mainly due to high viscosities). One of the most important technical challenges for Enhanced Oil Recovery (EOR) engineers is to develop an economical and feasible recovery process for heavy oil reservoirs. Depending on the reservoir-fluid system, commercial rates can be achieved by injecting (heat) steam. However, injectivity can be one of the key factors that can lead to difficulties to deliver enough heat to contact significant portion of the reservoir with steam (or for any other potential injectant). The main reason for such low injectivities in targeted heavy oil reservoirs originates from the excessively high in-situ oil viscosities. In order to facilitate the injection of reasonable quantities of steam in a continuous manner, cyclic steam injection techniques are often utilized at early stages of such projects, especially for extra heavy oil reservoirs. From the full project time cycle point of view, a combination of cyclic and continuous steam injection could be used to overcome this problem. In this paper, we have considered a five-spot pattern and studied optimum time for the conversion of cyclic steam injection to continuous steam injection for various type of reservoir and fluid properties using a commercial numerical simulator (STARS, 2009). To our knowledge, this is the first study that addresses the cyclic to contuinuous steam injection conversion time and correlates it to simple measurable quantities for the benchmark system with the reservoir/fluid properties selected.