An Integrated Approach for the Design of Squeeze of Mineral Scale Inhibitors

Abstract

Abstract Inorganic scaling is the process of mineral scale deposition that may occur in the well tubing, and/or in the near well bore area of both production or injection wells. Scale formation is usually the result of poor compatibility between the brines injected into the reservoir and the minerals in the formation. It may also be the consequence of abrupt pressure and temperature variations to which production fluids may be submitted between the reservoir and the surface. The precipitation of mineral deposits (carbonates, sulfates...) may create significant permeability impairments due to plugging of pore throats and thus induce large well productivity or injectivity losses. In most cases, precipitation cannot be avoided and preventive treatments are recommended. One of the most efficient treatment consists in squeezing a scale specific inhibitor into the formation. This paper presents an original integrated methodology aiming at defining the best chemical inhibitor formulation for a given application and at optimizing its implementation into the corresponding reservoir. Both experimental and numerical approaches are used to select the inhibitors, to evaluate their performance at both core and field levels and to define the best strategy for the squeeze process. Laboratory tests include the classical inhibitor selection methods based on jar tests and tube blocking tests but also on more sophisticated testing procedures recently developed. Numerical simulations of the treatment are performed using a in-house reservoir simulator to upscale the squeeze life time of the treatment from laboratory scale to well geometry. Introduction Scale inhibitor squeeze treatments provide one of the most common and efficient methods to prevent the formation of mineral scales in producering wells. Scaleing is an undesirable precipitation caused by either the mixing of incompatible waters or the rapid changes of the thermodynamic conditions during fluid production. The nucleation and growth of salt precipitates can occur in the production system or in the near wellbore formation. One of the most valuable techniques to prevent or to fight the scale formation is to inject, i.e. squeeze, a scale inhibitor directly into the formation. A typical squeeze treatment consists in injecting a slug of chemical product into the reservoir, followed by a well shut-in. During the shut-in period, the inhibitor is retained into the formation. When production is resumed, the inhibitor is released back into the produced water and prevents scale formation. The success of the treatment depends on how long the inhibitor concentration in the flowing water is efficient to prevent scale precipitation. This concentration has in fact to exceed the so-called Minimum Inhibitor Concentration (MIC). The focus of this paper is to review the items which contribute to a successful squeeze treatment, starting with the scale identification, followed by a laboratory study in reservoir conditions for the selection of the best inhibitor to prevent scale formation and ending with the design of the well treatment. Laboratory tests include the classical inhibitor selection methods based on jar tests and tube blocking tests but also more sophisticated testing procedures recently developed such as an electro-chemical method. These tests have for purpose to select the inhibitor on the basis of the MIC, which should be as low as possible. Then core floods are carried out in order to obtain the dynamic adsorption isotherm. Numerical simulations of the treatment are performed using a specific reservoir simulator to design the squeeze life time of the treatment, based on laboratory determinations of MIC and adsorption. This integrated methodology starting from laboratory testing to treatment design is illustrated on a case study where the scale consists of calcium carbonate deposition at the producing well. The paper is organized as follows. The first section is a presentation of the scaling problem. The second part describes the different experimental methods used for the MIC determination and the core flood tests. In the third section, we focus on the numerical simulations for the design of the treatment.