Abstract Drilling a long horizontal section within an ultra abrasive formation means short bit runs and high drilling costs. Despite many trials with standard technology bits in this gas reservoir in Algeria, the drilling performances were so poor that the profitability of the development project was greatly reduced. This paper describes the process to achieve the development of a specific bit design which eventually greatly improved the drilling performance in ultra abrasive sandstone formation and reduced the number of bits used. The problem analysis was based upon the evaluation of the bit performance history in combination with a full description of the physical characteristics of the rock. The abrasiveness of the sandstone was clearly the main factor which reduced the bit life, particularly in horizontal drilling. In order to increase the run length, the first objective was to reduce as much as possible the frictions of the bit cutting structure against the formation as well as to protect the bit gauge and heel. The analysis of the rock structure allowed to determine that despite its high abrasiveness, the sandstone presented a hardness weaker than expected. Therefore the penetration rate could be improved with a bit design aimed at favoring the crushing action. After developping two different bit designs and drilling three wells the rate of penetration and the footage were more than tripled. This is the result of a team work between the bit manufacturers and the operator.
Abstract Drilling through hard crystalline rocks like granites is challenging and taxing on the overall performance due to reduced rate of penetration (ROP). While efforts have been made in improving polycrystalline diamond compact (PDC) bits to increase ROP in hard rocks, the evidence of their field performance is currently restricted to only a few sites. There exists scope for alternative drilling technology where a significant fraction of hard rocks are present, such as in deep geothermal wells for electricity generation. In the ORCHYD project, two mature technologies – high pressure water jetting (HPWJ) and percussion drilling - were combined. A combination of bit profile and peripherical groove (slotted by HPWJ) creates a stress-relief effect releasing the rock from surrounding geological stresses, requiring lower energy to break the rock using a mud hammer. Furthermore, pressure waves due to percussion are reflected by free surfaces at the groove aiding in rock breakage. In this project, an experimental study on the influence of operating conditions such as HPWJ pressure, bottom hole pressure and surrounding geological stresses on the drilling performance was conducted. Several tests were performed at a dedicated drilling laboratory where the operational parameters can be varied to emulate drilling conditions for depths up to 4 km. As compared to tricone roller bits, ORCHYD technology guaranteed at least 4 times increase in the drilling performance. The performance of HPWJ in slotting a peripheral groove and mud hammer in rock breakage were strongly influenced by the operational conditions, e.g., for a given jet pressure the groove depth decreased significantly with increased bottom hole pressure. In this work, effects of such operating conditions on drilling performance were tested for different types of rocks such as Sidobre, Kuru Grey and Red Bohus. A sensitivity analysis of the influencing parameters on drilling performance of this technology is presented in this work. With increasing geological stresses, the proposed drilling technique is more effective in increasing ROP due to the stress relief effect. A novel technique combining HPWJ and percussion drilling using a mud hammer prototype was developed to show improved drilling performance in deep, hard rocks as compared to conventional drilling technique. Through this work, the performance of this method under different realistic drilling conditions was studied to optimize ROP, especially when drilling hard abrasive formations in deep oil and gas or geothermal wells.
ABSTRACT Geothermal energy is a leading candidate in fulfilling our transition efforts to a clean, sustainable, non-intermittent and renewable energy source. However, high drilling costs act as a showstopper in geothermal exploration. One of the main factors contributing to this high price is the drop in drilling performance when drilling through hard crystalline granite rocks that are usually found at depths greater than 4 km. Studies show that increasing the drilling performance by a factor of 4 with respect to the current drilling rates of 1-2 m/h can reduce the drilling costs up to 65%. Percussion drilling using down the hole (DTH) hammer has proven to be efficient in drilling through hard rocks. In ORCHYD project, we combine high-pressure water jet (HPWJ) with a DTH hammer to increase the rate of penetration (ROP) by a factor of 3 to 4. The HPWJ creates a peripheral groove in the rock surface facing the drill bit. This peripherical groove of few millimeters is expected to release the rock surface from the surrounding confining stress regimes – requiring lower energy to break the rock using percussion drilling. It is also expected that the free surface created by the groove aids in reflecting the waves created during percussion. A DTH mud hammer is modified to allow the flow of HPWJ through the hammer body and redirect it to the periphery of the drill bit. The prototype developed in this work was tested on a laboratory scale drilling test rig under realistic downhole drilling conditions. At the current stage of the project, it is demonstrated that slotting peripheral grooves using the HPWJ improves the ROP of the hammer drilling system by a factor of 2 to 2.5. INTRODUCTION Deep geothermal energy is a promising and increasingly important source of energy production worldwide. Geothermal electricity production is particularly attractive for both rich and poor economies due to its ability to generate both heat and electricity, which are in high demand. Enhanced Geothermal Systems (EGS) are becoming more popular as they allow for combined electricity and heat production at geothermal power plants (Angelone (2014)). However, drilling operations are a major component of the total project cost, representing up to 40% of the total cost (Angelone (2014)). For a 3 km well, the cost can reach up to 15 M€ (Angelone (2014)), which makes it challenging to extract geothermal energy in an economically viable manner.
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