Formation Damage Resulting from Biocide/Corrosion Inhibitor Squeeze Treatments

Abstract

To control sulfate-reducing bacteria (SRB) populations, and minimize operational problems noted in the water supply wells, a biocide/corrosion inhibitor squeeze program was applied. Because of the weak nature of the formation and potential sand production, an extensive core flood study was conducted to determine the effect of a commercial biocide (formaldehyde, nitrogen and phosphorous compounds) and a biocide-enhanced corrosion inhibitor on the permeability of reservoir core plugs. Core Flood experiments were conducted using reservoir core plugs at reservoir temperature (50 °C) and pressure (2000 psi). The results obtained indicated that high concentrations of the biocide or the biocide enhanced corrosion inhibitor caused up to 90% reduction in the initial permeability of reservoir cores. Several damaging mechanisms were identified: dissolution of the cementing material by the biocide (acidic), swelling of montmorillonite present in the formation and precipitation of calcium sulfate. Based on lab results, a detailed biocide squeeze treatment was designed to treat water supply wells. The treatment was able to control SRB populations while maintaining the integrity of the formation. This paper examines the design of the treatment and the results obtained from extensive lab testing and field trials. Introduction Seventeen wells were drilled in a shallow aquifer to supply water for injection in an oil field in central Saudi Arabia. The sandstone aquifer contains 1.4 to 2.1 wt% clay minerals (Table 1). XRD analysis of the clay-size (i.e., less than 2 microns) fraction indicates that kaolinite (migratable clay) and montmorillonite (swelling clay) are the two dominant clay minerals present in the formation (Table 2). The aquifer water has a total dissolved solids (TDS) content of 16000 - 24800 mg/L, depending on location within the field.1 The water contains significant amount of sulfate ion that varies from 3000 to 6000 mg/L. Table 3 gives the chemical analysis of the water produced from three wells in this aquifer. Oxygen content of the water is below detection (less than 5 ppb). In addition, iron content is less than 5 mg/L. Tests performed on the water produced from these wells indicated that they are contaminated with SRB, with population densities as high as 104 per mL detected. The presence of SRB has caused corrosion products (iron sulfide) and biomass to accumulate around the screens, which resulted in reduced well productivity and deterioration in produced water quality.2–4 Well completion. Completion of the wells producing water from this aquifer includes a perforated 7" casing, placed uncemented in a 8.5" hole. Because the aquifer sandstone is poorly consolidated, stainless steel wire-wrap screens were used for sand control.2 The screen-wrapped perforated casing is generally distributed in sections across the producing zone of the aquifer. The screens have a slot size=0.012", contributing to their tendency to trap fine particulate debris. The total depth of the wells is in the range of 4000 to 4200 ft. Aquifer pressure is low (1500 psi), necessitating the use of submersible pumps to produce water from this aquifer. Damage to water supply wells. Flow tests conducted just prior to field commissioning indicated a majority of the water supply wells could produce water at only a fraction of the required design rate. Water which was produced contained significant quantities of suspended solids, which were identified as a variable mixture of sand, clays, corrosion products and biomass. The results suggested the wells had been damaged by an accumulation of particulate solids. Previous studies2–4 detailed the impact of sulfate-reducing bacteria (SRB) on formation damage in these wells. Well completion. Completion of the wells producing water from this aquifer includes a perforated 7" casing, placed uncemented in a 8.5" hole. Because the aquifer sandstone is poorly consolidated, stainless steel wire-wrap screens were used for sand control.2 The screen-wrapped perforated casing is generally distributed in sections across the producing zone of the aquifer. The screens have a slot size=0.012", contributing to their tendency to trap fine particulate debris.The total depth of the wells is in the range of 4000 to 4200 ft. Aquifer pressure is low (1500 psi), necessitating the use of submersible pumps to produce water from this aquifer. Damage to water supply wells. Flow tests conducted just prior to field commissioning indicated a majority of the water supply wells could produce water at only a fraction of the required design rate. Water which was produced contained significant quantities of suspended solids, which were identified as a variable mixture of sand, clays, corrosion products and biomass. The results suggested the wells had been damaged by an accumulation of particulate solids. Previous studies2–4 detailed the impact of sulfate-reducing bacteria (SRB) on formation damage in these wells.

A Comprehensive Review of H2S Scavenger Technologies from Oil and Gas Streams

“…Unsaturated species of dialdehydes and diketones perform as better scavengers than alpha-beta unsaturated aldehydes and ketones such as 3-butene-2-one and acrolein because their performance results in a doubling of the activity usually exhibited per mole of H 2 S as well as releasing water-soluble products [77]. Edmondson [78] found that dialdehydes, mainly glyoxal, worked well when combined with a sulfite and a formaldehyde and yielded improved results. The chemistry of formaldehyde/ H 2 S reactions are shown in Fig.…”

“…For instance, hexamethylenetetraamine (HMTA) reacts with HCl, thereby producing formaldehyde. Although HMTA consumes a portion of the acid used and has a high efficiency for capturing H 2 S, it is still not as efficient as formaldehyde in scavenging of H 2 S [78].…”

Review and Evaluation of Corrosion Inhibitors Used in Well Stimulation

“…Stimulation of oil and gas wells using concentrated solutions of hydrochloric acid is a common practice; the acid that must be pumped through steel pumping equipment casing and production tubing prior to entering the formation, not only create damage to equipments, but also can damage the formation by corrosion by-products such as FeS and Fe(OH) 3 . Therefore, corrosion inhibitors are indispensible part of the fluid mix pumped downhole when a well is acidized (Nasr-El-Din et al, 2000).…”

Application of CE and CE-MS to Assay Corrosion Inhibitors Used in Well-Stimulation Treatments

“…4,5,31 Nasr-El-Din et al 32 investigated formation damage of sandstone reservoirs caused by the injection of corrosion inhibitors and biocide-enhanced corrosion inhibitors. Several authors highlighted the significance of varying the compositions and ratio of the acid inhibitor's components on the performance of the inhibtor.…”