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HDC chemistry was designed to remove barium compounds from oil and gas wells. As the chemistry evolved, two product lines emerged. HDC XREAM is the variant most effective at dissolution of barium, strontium and carbonate based scales. Although effective on some grades of mud barite, it is not as efficient as the Mark series. Typical field results yield up to 100 grams per litre of mixed scale components with barium sulphate yield from 45 g/l to 80 g/l. HDC Mark II is the variant tailored to dissolve mud grade barite and is effective in oil based and water based fluid environments. Depending on fluid environment and deployment barium sulphate yields can be expected to be from 40 g/l to 70 g/l.
The Working Principals For Open Hole Well Bore Cleaning Open hole well bore cleaning means precisely what the term implies in oilfield terminology: The removal of drilling fluid filter cake material and previously insoluble mineral complexes formed by contact and invasion of the well bore by drilling and or completion fluids, from an un-cemented and uncased off well bore. Open hole cleaning has become an issue with the advent of drilled, slotted and other un-cemented liner types and screen configurations. However, the chemical principals that led to the development of HDC as an open hole well bore cleaning system, evolved from the effective deployment of these fluids in the recovery of standard cased and perforated wells.
Typical Well Impairment Agents The weighting agents used in drilling fluids are the most common well bore contaminants by far. Barite and carbonate based drilling fluids by necessity carry large volumes of fine to medium fine solids into the well bore skin. Many of these particles become bridging agents effectively blocking production pore throats. These artificially added agents, in conjunction with naturally occurring drill solids become a lethal combination in the well bore. Mineral complexes are the next most common contaminant. Formed sometimes by contact with drilling fluid filtrates (or whole completion fluid), these also become problematical when oil/water or the gas/water contact levels coalesce. Composed primarily of calcium, magnesium, strontium, lead and barium compounds of sulphur or carbon, these minerals quickly lead to pore throat closure, tubular restriction and often full production or injection loss. Although a 3rd mechanism, that of emulsion blockage formed by incompatible oils and aqueous fluids is also quite common, as is asphaltine build up, these blockages are not as serious (relatively) as they are all commonly treatable with off the shelf de-emulsifiers and solvents. What separates the weighting agent/drilled solid contamination and the mineral complex contamination in the well bore from the asphaltine/emulsion block issues, is that no comprehensive system of effectively removing all these contaminants from the well bore has ever been developed.
Why Acids Don't Always Work It's almost a given in the oil industry that when production is impaired acid is pumped. More often than not, it's Hydrochloric Acid. The bottom line is that acids dissolve carbonates some of them but not all. They also have limited effect on sulphur compounds. So, if the impairment is from barite, strontium sulphate, or any of the scores sulphur based and amorphic forms of iron sulphide compounds that exist in the oil and gas production environment- that are not completely acidizable, an acid won't work.
Why HDC Fluids Work And Acids Do Not HDC dissolves calcium carbonate, calcium sulphate, strontium sulphate, magnesium sulphate, barium sulphate, lead sulphate, and some iron sulphide compounds. The bottom line is that HDC dissolves what Hydrochloric Acid does not and the much of the same material that it does dissolve.
Why HDC Fluids Work And Enzymes Do Not Enzymes work by reacting polymer (or other organic) material thereby generating acid by-products that dissolve preferential carbonate material only. Enzymes are simply another (less aggressive) way of delivering an acid.
HDC Cased Hole Cleaning Operations
Plugged Perforations and Near Well Bore Skin damage HDC can be applied to a number of cased hole scenarios. The method of deployment and the HDC variant fluid used all depend upon the down hole scenario existing at the time. Much essential information is needed before fluid selection can be made. Note* Different HDC and Ferrout formulations are referred to as variants. The term variant is used in this document to refer to the differing blends of these products which are used for widely differing application and density requirements.
Basic Information Requirements The following information is required in order to engineer a cased hole well bore recovery:
With the comprehensive knowledge of the well history in hand, Terra Expro can determine the best method to
The Product and Product Deployment Decision Tree Which chemical treatment is delivered to the problem zone is dictated by the contaminant composition. How the system is deployed is dependent on the downhole conditions and the state of the perforations.
Barite Settling Blocking Perforations If barite has settled and blocked the perforations milling is the most logical option. However, milling alone will not clean out the perforations neither will jetting. In this scenario milling becomes a circular operation, with the barite being effectively washed out, with much of it re-settling during the operation. The main problem with milling is the direction of flow. The flow, regardless of well orientation (vertical or horizontal) tends to be linear following the direction of the casing walls. When the milling or jetting head comes adjacent to the perforations the force of the fluid circulating actually compacts barite into the perforations and the tunnel beyond the casing/cement sheath.
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