TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractRasGas Company Ltd Drilling Task Force has instituted a new work process from ExxonMobil Development Company. This process is designed to optimize rate of penetration (ROP) in every foot of hole drilled. ROP limiters are systematically identified and eliminated during the drilling design, as well as during real-time well site operations.A central element in this work process is the real-time display and analysis of Mechanical Specific Energy (MSE). MSE is the calculated work that is being performed to destroy a given volume of rock. When a bit is operating at its peak efficiency, the ratio of energy to rock volume will remain relatively constant. This relationship is used operationally by observing whether the MSE changes while adjusting drilling parameters such as weight on bit (WOB) or rotary speed (RPM). If it remains constant while increasing WOB, the bit is assumed to still be efficient. If the MSE ratio increases significantly, either while drilling or while adjusting parameters, the bit has foundered. The driller then determines the most likely cause of founder and adjusts parameters accordingly. Adjustments continue to be made until the MSE value is minimized. The process of adjusting parameters is referred to as MSE testing. Recorded results of the driller's MSE tests are also used in post-analysis to guide redesign of the drilling system when ROP limiters are beyond the driller's control. In the North Field operations, downhole vibrations data were coupled with the MSE curves to further enhance the interpretation of the cause of founder and to manage drilling parameters.This paper presents examples from Qatar operations that demonstrate the manner in which MSE and vibrational data were used at the rig site to make operational decisions, and in post-drill analysis to redesign the system. Performance data is also provided to show the impact on operations. Performance improvements have varied by hole size, but range from 60 -380%.

Summary Significant performance improvement has been achieved by successfully managing drilling vibrations through bottomhole-assembly (BHA) redesign. This effort has resulted in increased footage per day and reduced tool damage. Prior literature has described improvements in operating practices to manage vibrations (Dupriest et al. 2005; Remmert et al. 2007) as a key component of this rate-of-penetration management process. In a parallel work activity, BHA redesign efforts have provided additional performance improvements of approximately 36% in one drilling application. Dynamic modeling of the BHA has identified the key design changes leading to these improvements. The redesigned BHA has lower calculated vibration indices than the standard BHA. The BHA design evaluation process uses a frequency-domain lateral dynamic model in both predrill forecast and post-drill hindcast modes. BHA lateral vibrations are characterized such that alternative BHA configurations may be developed and compared directly with a proposed baseline assembly. In the hindcast mode, the BHA model can be operated at the recorded weight on bit (WOB) and revolutions per minute (RPM) to generate corresponding model results in time or depth, and these values can be compared with the measured performance data. In one case study, the redesign of a BHA with downhole motor and roller reamer is described, with corresponding field data for four original BHAs and four redesigned assemblies. In a second application, model and field drilling results for two rotary-steerable assemblies are compared to evaluate the predictive ability of the model in smaller hole size and with different BHA types. Finally, the utility of the model to identify preferred rotary-speed "sweet spots" is demonstrated in a motor BHA operating in larger hole.

In March 2005, the operator implemented a rate of penetration (ROP) management process in Qatar's North Field. IPTC Paper 10706-PP describes the general principles behind the new work process and highlights its introduction to the operator. The ROP management process uses real time, customized surveillance technology to continuously maximize both drill bit cutter efficiency and transmission of energy from rig floor to the bit. This paper focuses on specific changes in drilling practices and their translation into substantive program acceleration and capital savings. To date, the development program has been accelerated by one year and USD 54 million has been saved while drilling 470,000 ft of hole. The process has proven to be a highly effective solution for management of drilling efficiency in a major development drilling campaign. As an indicator of program scope and effectiveness, over 440 personnel have been trained in mechanical specific energy (MSE) analysis, and 50 new field drilling records have been set by the nine rigs involved in the program. Importantly, the process has been implemented with one of the best safety records in industry (TRIR or total recordable incident rate of 0.11 per 200,000 man-hours as of September 06). Introduction The Qatar operator currently conducts drilling operations with nine rigs at eight platform locations across six very large producing blocks, each typically a 12 × 12 km concession. The majority of wells are drilled in batch mode by section, an approach adopted in the late 1990's when development drilling began. Over the years, the operator gained extensive field knowledge and developed many efficient operating practices. Thus, the introduction of any new ROP management process would be scrutinized and assessed against solid baseline operating performance. At the same time, 2005–2006 has been a period of transition, as the company increased rig count from three to nine rigs. The addition of many new support personnel in a multi-cultural working environment presented a significant challenge in terms of maintaining or improving drilling efficiency. This was coupled with high service personnel turnover, which continues to pose operational challenges. In the face of these challenges, it was decided to pilot test the ROP management process, with its first application in such an extensive carbonate field environment. The focus of the program was fourfold:conduct extensive, customized field training in MSE analysis;implement a standard surveillance program;introduce new practices in a phased manner concurrent with measurement of energy efficiency; andsystematically communicate learning across all rigs using MSE curves as the basis for discussion. This paper discusses summary learnings and offers technical examples of how MSE is being used to achieve consistently better drilling results. Specifically, the role of lithology, the general approach used to manage efficiency, ROP limiters encountered, and BHA optimizations will be discussed. While learning specific to the North Field is presented, the information is applicable to many drilling areas. Qatar North Field Background Figure 1 shows the location of the North Field offshore Qatar. Figure 2 shows both stratigraphy and typical wellbore configuration. Aside from one vertical data well at each platform location, all wells drilled by the operator are 55–65° S-shaped directional wells with an abbreviated drop section into the Khuff reservoir. Although platforms are kilometers apart, many wells are quite similar in terms of lithology, hole size, casing configuration, and casing setting points. An important reference data set when discussing MSE is rock unconfined compressive strength (UCS), presented in Figure 3. The MSE recorded while drilling should vary as the bit traverses rock of various strengths. However, it should only vary by the amount of change in rock strength. In field operations, a baseline MSE is established and any increase above this that exceeds the change in rock strength is likely to be an indication of bit dysfunction. The trending nature of MSE surveillance is described in IPTC Paper 10706-PP. It should be noted the efficiency gains described in this paper are only those directly attributable to the ROP management process in 17–1/2″, 12–1/4″, and 8–1/2″ sections.

TX 75083-3836, U.S.A., fax +1-972-952-9435. AbstractSignificant performance improvement has been achieved by successfully managing drilling vibrations through bottomhole assembly (BHA) redesign. This effort has resulted in increased footage per day and reduced tool damage. Prior literature has described improvements in operating practices to manage vibrations (1,2) as a key component of this ROP (rate of penetration) management process. In a parallel work activity, the redesign efforts have provided additional performance improvements of approximately 36% in one drilling application. Dynamic modeling of the BHA has identified the key design changes leading to these improvements. The redesigned BHA has lower calculated vibration indices than the standard BHA.The BHA design evaluation process uses a frequency-domain lateral dynamic model in both pre-drill forecast and post-drill hindcast modes. BHA lateral vibrations are characterized such that alternative BHA configurations may be developed and compared directly with a proposed baseline assembly. In the hindcast mode, the BHA model can be operated at the recorded WOB and RPM to generate corresponding model results in time or depth, and these values can be compared to the measured performance data.In one case study, the redesign of a BHA with downhole motor and roller reamer is described, with corresponding field data for four original BHA's and four redesigned assemblies. In a second application, model and field drilling results for two rotary steerable assemblies are compared to evaluate the predictive ability of the model in smaller hole size and with different BHA types. Finally, the utility of the model to identify preferred rotary speed "sweet spots" is demonstrated in a motor BHA operating in larger hole.