The term "dry" wellsite denotes a drilling operation without the use of an earthen reserve mud pit in land drilling, or without the overboard dumping of bulk drilling fluid in offshore drilling. As the two field practices have been increasingly scrutinized in environmentally sensitive areas, and the hauling off of bulk waste drilling mud is either too expensive or impossible to do, the minimum-volume control (source reduction) becomes an important part of drilling technology. This paper presents mechanistic and economic models of the controlled-volume drilling process and their theoretical use to design a "dry" location.

The mechanistic model quantifies all phenomena and operations related to drilling fluid as they affect the volume of waste mud and cuttings discharged from a wellsite. The model simulates the treatment of drilling process discontinuities (non-drilling operations) when rapid volumetric changes occur. Also presented is the steady-state model of "drilling ahead" operations with active mechanisms for drilling mud dilution, separation of cuttings, dewatering, and recycling.

The economic model involves a breakeven analysis of all components of the mud management process (i.e. mud making, maintenance, processing, and disposal) together with temporary storage requirements. A computer program simulating drilling and mud management processes relates drilling technology, field practices, local geology, and regulatory constraints to the volumes of active, stored, and waste mud and the costs of mud making, maintenance, and disposal. Investigated in the computer simulation study are volumetric effects of various parameters such as drilling conditions, dewatering unit performance, and solids control efficiency. The study shows that drilling can be designed and conducted in such a way that the wellsite discharge will be minimal.

Also presented is an example design of a dry drilling location where the cost of source separation technology (dewatering) is fully offset by the savings in disposal and mud costs. The study demonstrates that dry drilling locations are technically feasible and economically sound when designed using principles of volumetric control of the drilling mud. Also discussed is a mathematical model and design methodology for well-planning considerations.

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