Closed-loop drilling operations in environmentally sensitivity areas require integration of conventional solids control system with the chemically-enhanced centrifugation, a continuous dewatering process. The paper presents a design method for continuous dewatering. The method is based on the rigsite mud dewaterability testing and the breakeven cost economics.
The protocol for dewaterability test describes instrumentation and stepwise procedure to measure dewatering cake's moisture content and evaluate efficiency of volume reduction. Emphasized is preparation of weighted mud samples through removal of weighting material and correction for residual burite. The presented testing protocol eliminates volumetric measurements and replaces them with weight measurements which improve accuracy by an order of magnitude.
The paper explains how to use results from dewaterability tests to analyze cost efficiency of the dewatering component in closed-loop drilling operations.. The analysis is based upon all analytical model of breakeven cost. The model combines dewatering with depth-related quantities representing drilling progress and rates of waste generation, recycling and disposal. The paper shows: 1-How to evaluate dewatering performance while drilling: 2-How to set up technical requirements soliciting bids for dewatering services: and 3-How to predict drilling depth below which the process is not economical.
Continuous dewatering of drilling mud is a well site process for separating and recycling the mud liquid phase and minimizing the volume: of drilling waste. The process has been already patented [1] and used in field operations [2,3,4]. The analysis of published reports from these applications shows that economic performance of the dewatering process depends primarily upon three factors: 1-high cost of off-site disposal: 2-restricted disposal on-site (a ban on the annular injection, for example): and. 3-the degree of volume reduction attained through dewatering [5]. Therefore, any successful implementation or The dewatering process requires testing the mud dewaterability and combining the test results with cost factors to analyze process economics.
Dewaterability is the ability of a drilling fluid to release its water phase if subjected to mechanical expression. Before the expression, the drilling fluid has to be chemically conditioned in order to destabilize the suspension and free the water phase. (The design of chemical conditioning and its optimization has been described elsewhere [6].) Like other characteristics of drilling muds - the API filtration, for instance - dewaterability results from complex physical mechanisms but can be determined simply by measuring relative volume of released water and moisture content of the dewatering drilling fluid to calculate volume reduction efficiency EVB. The objective of this paper is to present the dewaterability testing procedure.
Currently, the only method for evaluation of dewatering performance is based on post-well or monthly recaps. In this method, cumulative volume of waste drilling mud is used to average cumulative expenditures and calculate the cost of dewatering per one barrel of waste mud [7]. Then, this cost is compared with the hypothetical disposal cost or the same barrel without using dewatering process. Finally a conclusion is made whether the use of dewatering would result in savings or losses.
