The Prediction of Interpretation of Downhole Mud Temperature While Drilling
- M. Thompson (Schlumberger Cambridge Research) | T.M. Burgess (Anadrill)
- Document ID
- Society of Petroleum Engineers
- SPE Annual Technical Conference and Exhibition, 22-26 September, Las Vegas, Nevada
- Publication Date
- Document Type
- Conference Paper
- 1985. Society of Petroleum Engineers
- 5.9.2 Geothermal Resources, 1.2.1 Wellbore integrity, 4.3.4 Scale, 1.6 Drilling Operations, 1.10 Drilling Equipment, 1.14 Casing and Cementing, 1.11 Drilling Fluids and Materials, 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc), 1.12.1 Measurement While Drilling, 1.6.1 Drilling Operation Management, 1.11.2 Drilling Fluid Selection and Formulation (Chemistry, Properties)
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The prediction of downhole mud temperature throughout all the operations of drilling has long been a clear objective, tackled by several previous authors. A method is given here for previous authors. A method is given here for performing this prediction in an accurate yet rapid performing this prediction in an accurate yet rapid manner which differs from all previous methods used and is suitable for extension to the interpretation of measurements downhole.
The problem lies in the coupling of the heat conduction in the formation, which can involve a lengthy solution process, with the heat convection in the mud, the numerical solution of which can suffer from non-physical instabilities in response to some of the fast changing conditions of rig operation. A justifiable approximation to the formation conduction reduces it to analytical form and a space transformation yields a stable solution procedure for the convection problem. Details are given of the equations used, the approximation involved and the space transformation which result in a computer model which is simple and fast in execution. Despite the speed. the model is comprehensive in terms of the drilling, circulating and static operations modeled and the complete specification of evolving well geometry and constraints.
The prediction method is validated by checking against recent field data of temperature measured downhole during drilling.
The speed of the model makes it feasible to consider its use for realtime interpretation of measurements downhole and a promising application would be the continuous determination of geothermal gradient. Thus the model described includes both predictive and interpretative aspects.
While drilling a well, fluid is circulated down the drillpipe and back up the annular space between drillpipe and rock. This drilling fluid (mud) has several functions such as cleaning the bit, transporting cuttings, balancing in-situ pore pressure and even lubricating the drillstring. One of the consequences is that at the bit the rock is generally cooled during the process of drilling and slow recovery back to the geothermal temperature only occurs when drilling and circulation cease.
Downhole temperatures as a result of drilling have long been of concern. There have been several published papers which include models of the drilling or mud circulating processes and others on the recovery of temperature after drilling has ceased. [refs 1, 2 and 3) . All these previous attempts have drawbacks which the approach previous attempts have drawbacks which the approach described here tries to circumvent.
Cementing is one of the operations which requires a knowledge of absolute temperature downhole and at present the estimated temperature is based on API present the estimated temperature is based on API recommendations which are derived from parametric fits on a few wireline measurements. A true predictive method would be a big advantage here, predictive method would be a big advantage here, especially in view of the large errors attributed to previous estimates.
|File Size||726 KB||Number of Pages||12|