An Investigation of New In-Situ-Generated Acid for Carbonate Mineral Dissolution in Sandstone and Carbonate Cores

Abstract

Matrix acidizing is a well stimulation technique in which an acid solution is injected into the formation to dissolve some of the minerals to recover or increase the permeability in the near-wellbore region. The most common acid used in matrix acidizing is hydrochloric acid (HCl). HCl has been used as a stand-alone stimulating fluid to decrease skin damage, create highly conductive wormholes in carbonate reservoirs, and stimulate sandstone reservoirs as a part of mud acid treatment. However, HCl in high-pressure/high-temperature (HP/HT) wells is problematic because of its rapid reactivity, resulting in face dissolution, corrosion, and associated increased inhibition costs.

Therefore, an acidizing system that is comparable to HCl in terms of availability and cost is required; however, the drawbacks associated with HCl, such as its fast reaction rate and high corrosion rate, should be taken into account in any newly developed systems. To answer these challenges, this study will investigate the effectiveness of a new in-situ-generated HCl acid (Urea Hydrochloride) that will provide slower reaction rates and lower corrosion rates in high-temperature reservoirs.

The objectives of this work are to investigate the performance of an in-situ-generated acid system as an alternative to regular HCl in the dissolution of carbonates in dolomite cores and in the preflush stage for sandstone cores, to identify the effect of additives on the outcome of the in-situ-generated acid system treatment, and to evaluate the effect of temperature on treatment outcome. The new in-situ-generated acid treatment will be applied to stimulate two types of sandstone cores (Grey Berea and Bandera) and Silurian dolomite. The effects of the treatment fluid at high temperature will be investigated based on results from coreflood experiments, chemical analysis of effluent samples, and X-ray computed tomography (CT).

This study’s outcome will assist in developing a more cost-effective and efficient design of acid treatments.