Water Frac Application in Injectors Improves Water-Flooding - An Innovative Approach

Abstract Fracturing in water injectors often becomes a pre-requisite to achieve the desired sweep efficiency. The requirement is more pronounced in the injectors with very poor injectivity or poor dissipation. Conventional stimulation techniques like acidisation have not proved to be beneficial. Under such circumstances, a recent foray has been made into the application of water frac. Water frac is an efficient technique to achieve a limited-length fracture, ensuring a higher sweep efficiency in water injectors. The candidate well is selected after a detailed study by multi-disciplinary team and a customized job schedule is prepared for an initial low-proppant concentration, followed by high concentration at the end to attain higher conductivity near wellbore. Due to zero polymer loading, this technique has the added advantage of low formation damage. There is also saving in chemical and proppant costs. This technique is suitable for not only water injectors, but also effluent disposal wells and polymer flood injectors. This paper describes the technique and requirements for water frac, along with the case histories. The job design and the results are discussed in details. The benefits accrued have underlined the success of this technique. Introduction The water injectors in the fields of western onshore oilfields in India occasionally suffer from low injectivity problem, resulting in poor pressure dissipation. This in turn affects the health of the nearby producers, as most of the fields are on water injection/ flooding scheme. Poor pressure dissipation at the injector end would be detrimental to the flooding efforts. Areal sweep efficiency is a key parameter for defining the success of any water flood program. A good areal sweep does not only ensure delayed breakthrough, but also increases oil recovery. So, in the western onshore fields of India, enhancement of injectivity is as desirable as the enhancement of areal sweep efficiency. In waterflooding, water is injected into some wells for pressure maintenance and oil is produced from some other nearby wells. In an areal sense (refer Fig. 1), injection and production takes place at points. As a result, pressure distributions and corresponding streamlines are developed between injector and the producers. In symmetrical well patterns, a straight line connecting the injector and the producer is the shortest streamline between them. As a result, the pressure gradient along this line is the highest and water moving along this line reaches the producer before water traveling along other streamlines. At the time of water breakthrough in producer, only a fraction of the reservoir area lying between is contacted by water, which is termed the sweep efficiency at breakthrough.