The analysis of chemical processes in reservoirs on the basis of the identification of injection-water fraction in produced brine

The time and subsequent evolution of injection-water breakthrough are two of the main indicators monitored by production chemists. After injected water breaks through, the risk of scaling may change significantly, and scale-mitigation procedures should be planned accordingly. The fraction of the injection water in the produced brine may be ascertained only from analysis of the produced-water samples. However, to date, there has been little discussion about other applications of injection-water-fraction tracking. In this paper, new applications that follow on from accurate knowledge of injection-water fraction are proposed. The calculated injection-water fraction may be applied 1. To quickly and accurately identify when injection-water breakthrough has taken place, at which time remedial action to prevent scale damage needs to be implemented. 2. To identify which ions are involved in in-situ geochemical reactions, and the degree of relative ion deviations (i.e., to identify ion-exchange reactions). 3. To detect the formation or formations from which a well is producing, and to determine (potentially) the amount of flow from each layer without the use of downhole flowmetering. Strong evidence of the involvement of barium, sulfate, and magnesium ions in reactions, on the basis of the calculations of the relative ion deviations, has been shown for field data. In another case, application of injection-water fraction prompted a re-evaluation of formation-water compositions, and as a result, it was discovered that the well was producing from a different formation after reperforation. The significant new developments presented in this paper allow analysts to obtain an indication of which ions are involved in the reactions, and the degree of relative ion deviations. Additionally, a technique is proposed that identifies the formation or formations from which the well is producing.