The relationships between oil based drilling fluid composition and the associated vapours have been quantified. This information will provide drilling Operators with improved control in the working environments. The study documents the long and short term changes in base oil selection and fluid compositions. The study is based on the generation and assessment of data collected from the vapour emissions of oil based drilling fluids with varying compositions and at a range of temperatures. Mineral oil based drilling fluid samples from the field have been investigated and compared to laboratory samples of similar basic composition. The impacts of other components in the drilling fluid formulations are also discussed. The purpose of the study was to enable a better understanding of the potential working environment hazards when using mineral oil based drilling fluids. One result of this understanding is that new rig construction designs, and older rig upgrades can be more informatively performed. Consequently this will reduce the repetition of continual modification costs.

The increasing necessity for hole enlargement while drilling (HEWD) technology has resulted in an essential need for engineers to fully understand the interaction between the drill bit and the hole opening tool. Inefficiency and damaging bit and bottom hole assembly (BHA) vibrations, caused by improper bit and reamer selection when drilling through interbedded formations and formation transitions, are a leading cause of inconsistent performance including excessive torque, low rate of penetration (ROP) and downhole tool failures (DTF). To mitigate vibrations, operators required a comprehensive analysis system/process that would allow them to model the complex BHA interaction in a virtual environment and quantitatively compare the performance of various design scenarios. To solve the challenge, the drilling team utilized a comprehensive, 4-D finite element model that couples laboratory results with a sophisticated computer simulator that calculates the drilling system’s dynamic performance from the bit back to surface in a real-time domain. Unlike other modeling programs that assume the contact forces between the cutter and rock, this advanced model utilizes exact cutting structure details coupled with the laboratory-derived rock mechanics to accurately predict the behavior of the bit and reamer with the entire drill string and bottom hole assembly. The effects of each specific BHA component and variations in drilling parameters on vibrations, ROP, and directional tendency can then be quantitatively evaluated.

Deepwater drilling often requires simultaneous hole-enlargement-while-drilling to improve project economics and efficiently deliver wellbore requirements. The challenge is to properly adjust reamer aggressiveness to match PDC bit dynamics to reduce damaging vibrations while maximizing overall drilling efficiency. Recent R&D efforts, focused on redesigning the BHA and optimizing drilling parameters, have successfully reduced bit/under- reamer vibrations. In addition, many operators and service providers have established rig-site procedures to recognize and mitigate vibrations. However, the results are still mixed and the lack of understanding the root causes of different vibrations is considered to be the major hurdle to improving drilling efficiency and performance. To solve this challenge an advanced dynamics model was developed which incorporates the following critical information: Mechanical rock properties (UCS) Bit/reamer design including cutter, body, gauge profile Physical characteristics of BHA components Formation characteristics (heterogeneous, anisotropy, interbedded) Well trajectory and borehole geometry Drilling parameters (WOB/RPM) This model can be applied to any drillstring configuration to provide BHA detailed information about RSS, PDM, PDC/roller cone, stabilizers, reamers, MWD/LWD and other downhole tools. This FEA model accurately predicts the drilling system's dynamics behavior from bit to surface and simulates the transient response of the entire system in time domain. Using this model, the combined effects of bit, reamer, BHA and drilling parameters have on vibration can be quantified and optimized before commencing field operations. This innovative technology provides an effective tool to optimize drilling performance without using the costly trial-and-error approach. An operator working in the Gulf of Mexico (GoM) required hole-enlargement-while-drilling to open a 12-1/4" pilot hole to 14- 3/4" from 13,000ft MD to approximately 20,000ft MD. The advanced drillstring dynamics model was utilized to optimize the BHA, bit and drilling parameters to minimize potential stick-slip and lateral vibrations. The optimization study, along with the operator's improved drilling practices, resulted in a 24% increase in penetration rate (ROP) compared to an offset well. Excluding the directional portions of the wellbore, the increase in ROP was calculated at 43%. The penetration rate increase reduced rig-time usage by 13.4hrs for a savings of $558,000USD.

Hole enlargement while drilling (HEWD) is an important technique in both deepwater and onshore drilling. Drilling interbedded formations is a difficult HEWD application. Two extreme cases can occur. One case is when the reamer drills in soft formation while the bit is in a harder formation. The other more difficult situation is when the reamer is in a hard formation while the bit drills ahead in soft formation. The latter creates an enormous challenge for the reamer to drill the harder formation without inducing large lateral and torsional vibrations which is detrimental to the reamer and other BHA components. An overall HEWD operating parameter management approach can greatly reduce probabilities of tool damage and unnecessary tripping while dramatically reducing drilling costs. A state-of-the-art BHA dynamic analysis program that allows modeling the reamer and bit in different formations plays a vital role in the overall HEWD management process. Before any planned HEWD operation, various possible operating scenarios can be virtually simulated through the BHA dynamic analysis program to evaluate the effect on BHA components of lateral and torsional vibrations. An optimized BHA configuration can be specified through these analyses and a set of optimal operating parameters for the chosen BHA can be developed. This paper presents an excellent case study of HEWD through severely depleted interbedded formations in the Gulf of Mexico. Previous offset wells had required multiple runs to HEWD this section due to reamer cutting structure damage. Models were constructed to compare performance with a range of BHA, WOB/WOR and RPM combinations. A set of optimal operating parameters and a road map were established for managing these parameters on the rig. Most importantly, the analyses recommended operating conditions that were substantially different from the accepted HEWD operation of increasing weight on bit (WOB) in harder formations. The analyses indicate that overall BHA performance was dramatically affected by weight on reamer (WOR). With a small sacrifice of ROP in the harder, more abrasive formations the HEWD system can effectively drill through the entire section without tripping due to component failure. This approach achieved excellent overall cost effective performance saving the operator $1.89 million on an offset well. Introduction The operator announced its field discovery in the Gulf of Mexico's Mars Basin in September, 2002. It is in 3,000ft of water, and is located approximately 88 miles southeast of Port Fourchon, Louisiana (Figure 1). During recent field development, the operator experienced problems with a BHA component. Specifically, the reamer 1,2 was suffering cutting structure damage driving up field development costs and slowing time to production. This paper will present the application challenges and resulting tool issues in addition to the problem analysis and engineering design changes to the reamer and operating parameters intended to solve the problem(s). Finally, the authors will present the results of applying the new technologies and operating parameters on the WELL #3 and how they saved the operator $1.89 million compared to costs incurred drilling the offset WELL #2.

Development of subsalt pay zones in deepwater GoM typically includes drilling long intervals of halite formation. Despite the relatively low UCS, salt drilling presents a unique challenge due to its plastic nature and tendency to creep. These factors coupled with complex deepwater casing programs necessitate the use of hole enlargement while drilling techniques. The difficulties of HEWD in salt is further magnified in deviated wellbores where maintaining the directional wellplan becomes a key performance objective.Using a 4D modeling program has resulted in improved HEWD ROP and directional control in salt on several deepwater GoM projects. The software allows engineers to model various RSS BHAs, optimize the bit/reamer cutting structure and prepare operating parameter recommendations tailored for the directional plan.Well A A Mississippi Canyon j-shaped well called for maintaining tangent at 44degrees through a 100% salt 14.5 x16.5 interval. Using a new reamer cutting structure design with a selected PDC allowed the operator to drill 7852ft at an ROP of 54.7ft/hr. The directional objective in the 12.25x14.75 interval of the same MC well was to hold tangent at 44 degrees before dropping to 15degrees. A new cutting structure design with a selected PDC was employed on the RSS/BHA. The 6022ft interval was drilled in one-run with an average ROP of 80ft/hr. Well BMaximum ROP was the primary objective in an 8877ft, 14.75x16.5 section of a s-shaped well which included building and holding at 35 degrees before dropping back to vertical in 100% salt. Bit and reamer recommendations and drilling parameter recommendations to maximize ROP were developed by calibrating the data from the offset well, Well A. The new cutting structure and pre-job planning resulted in a total run ROP of 97.5 ft/hr with an average on-bottom ROP of 129.1 ft/hr, an 80% improvement compared to offset.