System and method for estimation of drill cuttings concentration in a borehole
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Faster and cheaper wells are important to increase the recovery factor from producing fields and for making marginal fields profitable. Hole cleaning is a time consuming non-productive operation which increases well cost. However, insufficient hole cleaning can stop the drilling operation, reduce rate of penetration, or even lead to side tracking. Consequently, hole cleaning is necessary but time spent on unnecessary hole cleaning needs to be minimized. By knowing cuttings concentration in the annulus one can optimize time spent on hole cleaning, increase ROP or reduce hole problems related to hole cleaning due to a more optimal hole cleaning procedure. Today, there is no accurate and easy measurement system to obtain cuttings concentration in the annulus. This master thesis analysis two proposed methods for measuring cuttings concentration proposed in Fevang (2014) project thesis. The proposed methods calculate cuttings concentration based on equivalent static density, equivalent mud weight and cuttings bulk density. The thesis includes background theory and applies the proposed methods on data from six wells on the Norwegian Shelf. The analysis shows that the proposed methods can be used to estimate the cutting concentration (method 2) or the change in cutting concentration (method 1) under certain circumstances. The three major uncertainties in proposed method 2 is the accuracy of:1. The bottom hole assembly pressure gauge (maximum ±1.0 bar). 2. Gas fraction in the annulus during drilling of gas bearing formation. 3. Known fraction of lifted cuttings in high inclination wells. The four major uncertainties in proposed method 1 is the accuracy of:1. The pressure difference in the BHA (maximum ±0.5bar). 2. Constant gas fraction in the annulus.3. Constant temperature profile.4. Constant or known fraction of the lifted cutting in high inclination well. Further work include applying simulated- temperature profile and fraction lifted cuttings to the proposed methods and compare results with a simulated method or other method for measuring cuttings concentration.