Acid-Sludge Characterization and Remediation Improve Well Productivity and Save Costs in the Permian Basin

Abstract

Many oil wells in the Permian Basin have reported sludging problems associated with acid stimulations. The acid sludge is similar among wells and was identified as a viscous emulsion stabilized by asphaltene-rich organic solids. The sludging tendency of the oil increased with the concentrations of asphaltenes and resins, base number of the oil, and ferric ion content in the acid. Only three out of nine commercial acid systems tested were effective in preventing acid-sludge formation; they all use the same novel iron control technology, Le., catalytic reduction of ferric ions. Several commercial and generic solvent systems were effective in dissolving acid sludge, including mixtures of an aromatic solvent (e.g., xylene) with either isopropyl alcohol (2: 1 volume ratio), or ethylene glycolmonobutylether (EGMBE) (2: I to 3: I volume ratios). Selection of acid formulations and solvent systems was based on cost effectiveness and operation safety. Field implementation proved successful. If the results of this study had been implemented earlier in the lives of some of the Permian Basin properties, the recovery of 574 BOPD of lost or deferred production from 99 wells could have been realized. This would have resulted in an estimated increased revenue of over U.S. $3 million in I year.

A Multifaceted Approach for Controlling Complex Deposits in Oil and Gas Production

“…This acid uses reducing agents such as erythorbic acid and ammonium mercapto acetate. Wong, Hwang et al (1997) studied a number of Permian Basin crude oils known to cause formation of acid sludge and compared nine different anti-sludging formulations. They found that ferric iron control was necessary and recommended a "catalytic reducing agent."…”

Experimental evaluation of sandstone stimulation fluids for acid sludge prevention during oilwell matrix stimulation jobs

“…To begin with, as crude oil components and sample age are part of the multiple factors influencing sludge-forming tendencies [2,6], experimental tests were conducted as soon as the sample focus of this study was received in the laboratory. The first step was fluid characterization including BSW, API gravity and asphaltene content measurements as shown in Table 1.…”

“…During acid stimulation treatments, it is highly possible that acid-sludge aggregates appear, they are recognized as acid or oil insoluble products [1] originated from interactions between treatment fluids and some sorts of crude oils [2]. These insoluble particles can be present as a stable emulsion, solids, or a combination of both [2] and they are deeply associated to asphaltenic components present in crude oils, which are normally in colloidal state, and that are mainly destabilized by low pH environments once they are exposed to the acid treatment [2]. However, there are some other factors associated to sludge occurrence including but not limited to acid type or strength, presence of Ferric or Ferrous ions, mutual solvents, acid corrosion inhibitors [3] and as mentioned, chemical structure of crude oil [4].…”