First Experience Matters: Evaluation of Acid Treatment Recipe for Fines Migration Control in S Field Sandstone Reservoirs

Abstract

Restoring formation damage by acid matrix treatment in sandstone formations faces multiple challenges due to variable petrophysical and compositional properties. The S field team had carried out a formation damage study to determine the damage mechanism, evaluate the best acid treatment recipe to treat the formation damage mechanism identified and study the effect on petrophysical properties before and after the treatment. Most of the S field oil producers experienced rapid decline in production, and this is suspected to be due to fines migration and plugging. The formation damage study is divided into three sections: the field background review, the potential formation damage identification, and the evaluation of the best acid treatment recipe for S field formations. Core samples from a wide range of mineralogy, permeability, pore distributions and porosity were evaluated using laboratory testing to describe the elemental and morphological presence of each mineral. Then, four of the core samples were high graded for evaluating the permeability by flooding with brine and oil to examine the fines migration and dispersion potential of clays and siderite. The next phase of this study was continued with the core sample acidization using organic acid and HCl to identify a suitable acid treatment cocktail. This will be discussed in detail in this paper. Fines migration was observed to be resulted from movement of both siderite and aluminosilicate clays under representative conditions. The evidence from the geological analyses and core flooding shows that in brine, there is a tendency for siderite to migrate, potentially even at low flow rates. The effect is expected to be more severe in brine than in oil and possibly in both phases. HCl acid and strong organic acid treatments with and without the presence of an iron control to remove iron carbonates in siderites and iron-silicate gel formation will be outlined in this paper. The result of the HCl treatment was that it was able to remove carbonate material from the core, but it was still not able to substantially improve wellbore permeability. An additional short phase of testing examining a HF-HCl package was demonstrated more effective and is discussed extensively in this paper. This laboratory work is not unusual to the sandstone stimulation however the discussion of the core flood testing findings and acid recipe comparative study provides more comprehensive understanding on the effect of fines migration to the success of the stimulation treatment and its effect on petrophysical properties. The outcome of this work will lead to a reliable design of sandstone matrix acid treatments and, increase the acid stimulation treatment success rate which subsequently optimizes well productivity.