Drilling fluids impact

The choice of drilling fluid has a major impact on the evaluation and" production of a well. Later in this section, we will investigate the interaction between drilling fluids, logging operations and the potential damage to well productivity caused by mud invasion into the formation. 

Chromium lignosulfonates are the biggest contributions to heavy metals in drilling fluids. Although studies have shown minimal environmental impact, substitutes exist that can result in lower chromium levels in muds. The less used chromium lignites (trivalent chromium complexes) are similar in character and performance with less chromium. Nonchromium substitutes are effective in many situations. Typical total chromium levels in muds are 100-1000 mg/1. 

Polyacrylates are often added to drilling fluids to increase viscosity and limit formation damage. The filter-cake is critical in preventing reservoir invasion by mud filtrate. Polymer invasion of the reservoir has been shown to have a great impact on permeability reduction [98]. The invasion of filtrate and solids in drilling in fluid can cause serious reservoir damage. 

V. Garg, M. Ralhan, H. C. Tewari, A. Srivastava, S. K. Nanda, and H. S. Rawat. Impact assessment of solid lubricants used in drilling fluids on the producing zone. In Proceedings Volume, volume 3, pages 55-60. 1st India Oil Natur Gas Corp Ltd et al Int Petrol Conf (Petrotech 95) (New Delhi, India, 1/9-1/12), 1995. 

Of even more economic importance is the rheological impact of the addition of KC1 to conventional water-base drilling fluids. KC1 causes undesirable increases in both yield point and gel strength that can only be eliminated by chemical disperants or by dilution with fresh water. Dilution in turn requires more KC1 for clay inhibition, and the cycle continues with mud costs escalating exponentially. 

Neff, J.M., McKelvie, S. and Ayers, R.C. Jr (2000) Environmental Impacts of Synthetic Based Drilling Fluids, report prepared for MMS by Robert Ayers 8c Associates, US Department of the Interior, Minerals Management Service, Gulf of Mexico OCS... 

Friedheim, J.E. and Pantermuehl, R.M. (1993) Superior performance with minimal environmental impact a novel non-aqueous drilling fluid. SPE 25753 SPE/IADC Drilling Conference 23-25 February 1993, Amsterdam. Society of Petroleum Engineers, Richardson, TX, pp. 713-726. 

There is increasingly a fifth function that must be met, namely, to minimize the environmental impact of the drilling fluid and the drilled... 

Synthetic-based muds are mineral oil muds in which the oil phase has been replaced with a synthetic fluid, such as ether, ester, PAO, or linear alkylbenzene, and are available from major mud companies. The mud selection process is based on the mud s technical performance, environmental impact, and financial impact. Synthetic muds are expensive. Two factors influence the direct cost unit or per-barrel cost and mud losses. Synthetic muds are the technical equivalent of oil-based muds when drilling intermediate hole sections. They are technically superior to all water-based systems when drilling reactive shales in directional wells. However, with efficient solids-control equipment, optimized drilling, and good housekeeping practices, the cost of the synthetic mud can be brought to a level comparable with oil-based mud [1308]. 

Norman, M Ross, S., McEwen, G. and GetlifF, J. (2002) Minimizing environmental impacts and maximizing hole stability - the significance of drilling with synthetic fluids in New Zealand. New Zealand Petroleum Conference Proceedings 24—27 February 2002. 

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