Operators face the continuing challenge to improve drilling efficiency for cost containment, especially in deepwater drilling environments where drilling costs are significantly higher. Innovative drilling technologies have been developed and implemented continuously to support the initiative. In many areas of the world, including the Gulf of Mexico (GOM), hydrocarbon reservoirs exist below thick non-porous and impermeable sequences of salt that are considered a perfect cap rock. However, salt poses varied levels of drilling challenges due to its unique mechanical properties.
At ambient conditions, the unconfined compressive strength (UCS) of salt varies between 3,000 to 5,000 psi; however, the strain at failure for salt can be an order of magnitude higher when compared to other rocks. Consequently, during drilling salt's viscoelastic behavior requires that its must be broken with an inter-crystalline or trans-crystalline grain boundary breakage. When compared to other rock types, the unique isotropic nature of salt results in a level of strain that is much higher for the given elastic moduli. This strain level makes salt failure mechanics different from other rock types that are prevalent in the GOM.
Hybrid bits combine roller-cone and polycrystalline diamond compact (PDC) cutting elements to perform a simultaneous on-bottom crushing / gouging and shearing action. Two divergent cutting mechanics pre-stresses the rock and apply high strain for deformation and displacement, resulting in highly efficient cutting mechanics. To meet the drilling objectives, different hybrid designs have been implemented to combine stability and aggressiveness for improved drilling efficiency. An operator, while drilling salt sections at record penetration rates, has successfully used this innovative process of rock failure utilizing the dual-cutting mechanics of hybrid bits. This has resulted in significant value additions for the operator.
This paper analyzes field-drilling data from successful GOM wells and attempts to correlate salt failure mechanics and provide insight into dual-cutting mechanics and its correlation with salt failure. The paper also reviews the drilling mechanics of hybrid bits in salt and highlights importance of dual-cutting mechanics for achieving higher penetration rates in salt through improved drilling efficiency.
The Bakken and Niobrara operator will eliminate 254 jobs in an effort “to better align [its] business with the current operating environment.” Oilfield flares are a bright indicator of rapidly rising oil production that exceeds pipeline capacity. And it raises the question: Why are oil companies in such a hurry? How Close Is Too Close? The ideal well spacing is in the eye of the beholder.
The shale sector is making moves to consolidate amid investor pressure to increase cash flow. This deal will form the second-largest producer in Colorado’s DJ Basin. PDC’s president and CEO describes the company’s management strategy for its hydraulic fracturing operations in the Wattenberg Field and the Delaware Basin. Baker Hughes is developing a drill bit capable of auto-adjusting its depth-of-cut feature to handle dynamic drilling conditions. Drilling the Severnaya Truba field in Aktobe, Kazakhstan, has been costly and time consuming.
Regardless of how good a new product or method may be to a drilling operation, the result is always measured in terms of cost per foot or meter. Lowest cost per foot indicates to drilling engineers and supervisors which products to use most advantageously in each situation. Reduced costs lead directly to higher profits or the difference between profit and loss. For those in administration, engineering, manufacturing, and sales, cost calculations are used to evaluate the effectiveness of any product or method, new or old. Because drilling costs are so important, everyone involved should know how to make a few simple cost calculations.
Bit classification allows efficient selection and use of polycrystalline diamond compact (PDC) and diamond drill bit. The classification system currently in use was developed by the International Association of Drilling Contractors (IADC). IADC classification codes for each bit are generated by placing the bit style into the category that best describes it so that similar bit types are grouped within a single category. The version currently used was introduced in 1992 using criteria that were cooperatively developed by drill-bit manufacturers under the auspices of SPE., The system leaves a rather broad latitude for interpretation and is not as precise or useful as the IADC Classification System for Roller-Cone Bits. It does not consider hydraulic features incorporated into a bit and does not attempt to give a detailed description of body style beyond basic classification of the overall length of the bit cutting face.
The bearing, seal, and lubrication systems of a roller cone bit are important aspects of bit life and efficiency. Roller cone bearing systems are designed to be in satisfactory operating condition when the cutting structure of the bit is worn out. To achieve this standard of bearing performance, modern goals for seal and bearing system life are 1 million or more revolutions of a bit without failure, as opposed to 300,000 or fewer in the recent past. To achieve this goal, research into bearing, seal, and lubricant designs and into materials that improve seal and bearing life is ongoing. Roller-cone bits primarily use two types of bearings: roller bearings and journal bearings, sometimes called friction bearings.
The shape of a Polycrystalline Diamond Compact (PDC) bit body is called its profile. It is also the principal influence on bit productivity and stability. The geometry established by the profile contributes to hydraulic flow efficiency across the bit face. Hydraulic flows directly influence ROP through the cuttings removal they provide. If cuttings are removed as rapidly as they are produced, ROP will be relatively higher.
Principles for Polycrystalline Diamond Compact (PDC) bit design are discussed here. Each of these factors must be considered on an application-to-application basis to ensure achievement of rate of penetration (ROP) goals during cooling, cleaning the bit, and removing cuttings efficiently. During design, all factors are considered simultaneously. Cutting structures must provide adequate bottomhole coverage to address formation hardness, abrasiveness, and potential vibrations and to satisfy productive needs. Early (1970s) PDC bits incorporated elementary designs without waterways or carefully engineered provisions for cleaning and cooling.
Various Polycrystalline Diamond Compact (PDC) bit configurations are discussed below. The term "diamond bit" normally refers to bits incorporating surface-set natural diamonds as cutters. This bit type, which has been used for many years, was the predecessor to PDC bits and continues to be used in certain drilling environments. Diamond bits are used in abrasive formations. They drill by a high-speed plowing action that breaks the cementation between rock grains.