Factors that affect downhole temperature while drilling (TWD) were modeled with a comprehensive in-house drilling mechanics and hydraulics model to help explain field observations in a GoM deepwater well. In a long, near-horizontal well section, the TWD from measurement while drilling (MWD) was much hotter than the surrounding formation temperatures, an important issue due to observed dependence of reduced bottom-hole temperature (BHT) and lost-circulation events, and also effects on downhole tools and non-productive time (NPT.) The model used is an in-house suite of drilling modules capable of modeling hydraulics, torque and drag, drillstring dynamics, and their interactive effects. Heat generation and temperatures are calculated in a coupled manner, by considering factors that include:○Mud-formation heat transfer and mechanical friction of the drillstring against the formation/casing wall;○Heat from pressure drop across bit nozzles, and the mechanical rock cutting action of the drillbit;○Friction in all drilling situations - making hole, tripping etc, depending on annular clearance;○Heat generation from mud-motor operation and operating inefficiencies. Results indicate that the rotary speed is very important; the higher the RPM, the more the BHT increases. The annular clearance is also a strong factor; the less the clearance, as in casing/liner drilling (CLD) or from tight-clearance downhole tools, the higher the BHT. Other factors in varying degrees of importance are flow rate, mud type, and weight on bit. Results of this work will support on-going attempts at deepwater NPT reduction. Introduction and Background Deepwater drilling is fraught with challenges, including borehole integrity and lost circulation. Investigators (Ref. 1–3, among others) have identified temperature effects as contributing to hoop stress increase and lost circulation mitigation. This is important because in tight drilling margins, ECD management within the pore-pressure/fracture-gradient window can be difficult, and one may possibly resort to novel methods of increasing the fracture gradient. In this paper, we have used a comprehensive in-house drilling mechanics model, along with field data and published experience, to investigate factors that affect well BHT with a view to potentially controlling these factors in order to manage the BHT and reduce lost-circulation events. The example well is in deepwater Gulf of Mexico (GoM) where relatively cold formations often experience lost circulation. Fig. 1 illustrates this vividly where mud losses were observed in zones with reduced temperature, all other factors remaining the same. Fig. 2 shows a temperature-trend match for a section of the well with TWD data. The data scatter is related to pipe connection events, rotating and non-rotating modes, changes in circulation rates, etc. On the other hand, formation temperature decrease through salt zones helps reduce salt movement (creep) and tar flow. Though critically important to NPT management in subsalt wells, the low-temperature effect along with salt-induced casing collapse is outside the scope of this paper. Work is underway on these technologies.

With well depths more commonly surpassing 30,000 ft below the mudline and ever-increasing water depths, exceedingly high-pressure environments present a new and challenging frontier for both operators and service companies. These new environments demand advances to existing technology to endure such pressure extremes while also accurately positioning the wellbore in the reservoir and obtaining critical geological information as the well is drilled. A recent example in this pressure regime in the deepwater Gulf of Mexico will be reviewed. Pressure limits of the currently available technology are extended while successfully meeting drilling and evaluation goals. The drilling and evaluation technologies delivered real-time formation pressure and geological information, along with continuous directional control, enabling the operator to make vital decisions while drilling and for sidetrack evaluation. This real-time decision-making capability reduced the time required to execute casing point selection and subsequent sidetrack plans. Emphasis is placed on the need for operators and service companies alike to focus on thorough pre-job planning while paying close attention to complete system requirements high-pressure evaluation tools and detailed reviews. Newer drilling opportunities, particularly in the deepwater arena, involve operating in extreme environments such as ultrahigh pressures, and demand different approaches to ensure flawless execution. This paper presents the variety of challenges, critical success factors, and lessons learned when drilling these ultra-high pressure wells in the demanding waters of the Gulf of Mexico. With downhole pressures approaching 30,000 psi and ever-increasing rig costs, the need for dependable drilling systems and integrated advanced formation evaluation technology is needed now more than ever. The case results showcase the ability to set a new performance standard, extend the conventional operating envelop farther, and deliver answers while drilling.

Two new benefits derived from the use of a Universal Fluid (UF) have been demonstrated:reduction of the hole washout volume andsolidification of excess drilling fluid and drill cuttings for environmentally acceptable on-site waste disposal. A UF containing about 30 lb/bbl blast furnace slag was used as a drilling fluid while drilling a recent south Louisiana well in an effort to reduce hole washout and to demonstrate that the solidification of the UF and drill cuttings would provide an environmentally safe material which remains on-site and can be used for location maintenance, road construction, and land fill or other uses. The UF was used while drilling a 9 7/8-in. hole from 3,125 ft to the casing depth of 10,600 ft. The slag content ranged between 25 and 30 lb/bbl, while the UF weight was increased slowly from 9.4 lb/gal to 12.2 lb/gal. Caliper logs indicated that the average diameter of the UF-drilled section was 10.88 in., considerably better than the 12.85 in. of the same section of a previously drilled offset well. Of the total 147,000 lb of slag used, about 30% remained in the UF, about 22% was deposited as filtercake, and about 21% was discharged with the cuttings through solids control equipment. A concept of rig-site drilling waste management involving solidification of the UF wastes is elaborated and related lab and field data are presented. The necessary amount of slag for solidification is already in the UF and solid wastes, but additional slag can be added depending on the final product firmness desired. To demonstrate the waste solidification process, an additional 20 lb/bbl slag was mixed with a 40-barrel batch of the excess waste in a "V," -bottomed auger tank. The UF mixture was allowed to harden on location and successfully used for land fill. This paper shows that the UF can protect the drilled wellbore and can be economically treated and used for on-site disposal. P. 785