No abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. ProposalBarite is a common weighting agent used for oil well applications. It is commonly used to provide adequate weight to control downhole pressures in drilling slurries. Since it is used for control of pressure, it is a common source of formation damage, especially in deep, hot formations where drilling fluid weights exceed 17 ppg. Although alternatives do exist for barite, (e.g., formate drilling fluids) they are significantly more expensive, and not available on a rapid turnaround basis as in emergency situations required by well control operations. Once damage has occurred, remediation is a very difficult proposition. Barite is not soluble in typical oilfield inorganic acids used in stimulation. The most common methods of remediation are fracture stimulation and/or deep perforations. The use of these methods can remediate the problem, but at high cost. Also, since the well productivity cannot be evaluated prior to stimulation operations, a poor quality well cannot be identified until a significant investment has been made.The most common chemicals currently in use to address this problem are "barite dissolvers". These agents are all strong metal ion chelators. Aminopolycarboxylic acids (e.g., EDTA) and similar reagents have been used with low success rates. 1 Recently, hydroxylaminopolycarboxylic acids were introduced, but to the best of the author's knowledge was not extensively used in the field. 2 This study investigates a new barite dissolver and compares its performance with other commercial dissolvers. The new material is a proprietary dissolver supplied in a liquid form. This study investigates the dissolving capacity, and evaluates the effectiveness of the dissolver by conducting coreflood tests. These tests were conducted using sandstone cores obtained from a deep gas well (300ºF). The effectiveness of the dissolver was followed by measuring the concentration of barium in the core effluent. Unlike other barite dissolvers, the new chemical is shown to be very effective in restoring the permeability of damaged cores. The new chemical does not require long soaking times, and does not induce fines migration due to chemical means.

Combining scale inhibition with matrix stimulation in a single treatment has always been a challenge due to potential formation damage. This concern has been historically prominent in carbonate reservoirs, due to the accelerated precipitation of the scale inhibitor at very low pH values. Earlier experience in combining acid stimulation with scale inhibition in carbonate reservoirs has been reported with limited success.This paper presents recent development in combining acid stimulation and scale inhibition treatments in sandstone and carbonate reservoirs. The combined treatment utilizes a newly developed scale inhibitor (a polymer-based inhibitor) that offers full compatibility with a wide range of the commercially available acidizing systems, including hydrochloric acid, mud acids and chelating agents.This treatment minimizes the number of well interventions, significantly reduces well maintenance cost and improves the work-over efficiency. At least one scale inhibitor squeeze treatment is eliminated with every acid stimulation treatment. In addition, there are other inherent advantages including: effective inhibitor placement and better coverage of the target zone.