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Hole deviation is the unintentional departure of the drill bit from a preselected borehole trajectory. Whether it involves drilling a straight or curved-hole section, the tendency of the bit to walk away from the desired path can lead to drilling problems such as higher drilling costs and also lease-boundary legal problems Figure 1 provides examples of hole deviations. It is not exactly known what causes a drill bit to deviate from its intended path. It is known that some resultant force acting on a drill bit causes hole deviation to occur. The mechanics of this resultant force is complex and is governed mainly by the mechanics of the BHA, rock/bit interaction, bit operating conditions, and, to some lesser extent, by the drilling-fluid hydraulics.
Introduction Directional drilling is defined as the practice of controlling the direction and deviation of a wellbore to a predetermined underground target or location. This section describes why directional drilling is required, the sort of well paths that are used, and the tools and methods employed to drill those wells. A directional well can be divided into three main sections--the surface hole, overburden section, and reservoir penetration. Different factors are involved at each stage within the overall constraints of optimum reservoir penetration. Most directional wells are drilled from multiwell installations, platforms, or drillsites. Minimizing the cost or environmental footprint requires that wells be spaced as closely as possible. It has been found that spacing on the order of 2 m (6 ft) can be achieved. At the start of the well, the overriding constraint on the well path is the presence of other wells. Careful planning is required to assign well slots to bottomhole locations in a manner that avoids the need for complex directional steering within the cluster of wells. At its worst, the opportunity to reach certain targets from the installation can be lost if not carefully planned from the outset. Visualizing the relative positions of adjacent wells is important for correct decisions to be made about placing the well path to minimize the number of adjacent wells that must be shut in as a safety precaution against collisions. The steel in nearby wells requires that special downhole survey techniques be used to ensure accurate positioning. This section is generally planned with very low curvatures to minimize problems in excessive torque and casing wear resulting from high contact forces between drillstrings and the hole wall.
The most common deviation tools for directional drilling are steerable motor assemblies (or so-called positive-displacement motors [PDMs]) and rotary steerable systems (RSSs). Adjustable-gauge stabilizers, known as "2D rotary systems," have become quite popular to run with the rotary and PDM assemblies to control inclination. Whipstocks, especially casing whipstocks, are used routinely to sidetrack out of cased wellbores. Other tools, such as turbines, are used mainly in Russia, and jetting bits are seldom used today. The most important advancements in trajectory control are the steerable motor assemblies, which contain PDMs with bent subs or bent housing.
The Gulf of Suez includes good source rocks for hydrocarbon generation; the Sinai field-Abu Rudeis base is the most important and largest producing field in this area. This formation represents the most challenging case study with significant amount of clays that affect the hydrocarbon production. A clay stabilizer additive was introduced during a workover operation and was determined to provide promising results. These results include better fines migration and prevention of swelling and migration while leaving formation and fluid properties unchanged.
As with all clay stabilization products, a critical factor for treatment success is providing protection against clay swelling. Most gas wells in North Africa formations contain freshwater-sensitive clay minerals, including those found in shale streaks and pore throats. Complex clay minerals in these formations can create difficulties during drilling or workover operations. While the bottomhole assembly (BHA) is being replaced and flowback stopped, fresh water soaks into the formation for longer durations, resulting in longer contact with clay minerals. This can create a multitude of problems associated with clay swelling, including formation damage.
This paper describes a clay stabilization additive that adheres to the clay surface and provides clay swelling and fines migration control, reduced friction, and decreased hydrostatic pressure when exposed to a freshwater-based fluid system. The product was evaluated in the laboratory using various core samples from Field A. During this evaluation, X-ray diffraction (XRD), X-ray fluorescence (XRF), linear swell meter (LSM), and capillary suction time (CST) assessments were performed. The clay stabilizer showed excellent results. This additive use can help to increase the efficiency of downhole motors and drill bits as a result of low friction pressure. This new stabilizer does not require special equipment, like other salts; consequently, it reduces time required for mixing while pumping. In addition, the blend is mixed at a lower concentration, which helps to solve logistical challenges, making it more efficient at a lower cost than salts.
The clay stabilizer discussed provides permanent protection with no effect on original permeability. In addition, the low concentration of the clay stabilizer showed better performance in LSM and CST.
Abdel-Aal, Mohamed Ahmed (MODUS) | Mohamed, Fahd Mohamed (MODUS) | Abdelkader, Ahmed Galal (MODUS) | AbdulLatif, Mohammed AbdulHamid (MODUS) | Koulidis, Alexis (King Abdullah University of Science and Technology) | Ahmed, Shehab (King Abdullah University of Science and Technology)
Well drilling and wellbore conditioning typically involve multiple specialized drilling tools. Systematic application of such tools can be a challenge from a logistics and maintenance perspective, which eventually has an impact on the efficiency of the drilling process as well as the resulting wellbore condition. This paper presents a new multifunctional drilling tool developed to address such operational challenges. The tool’s effect on the drilling and logging process is illustrated through a field case study.
The CRS is a multifunctional drilling tool able to Cut, Ream and Stabilize when installing in a BHA. It is envisioned as an integral bottom hole assembly (BHA) component replacing the uppermost stabilizer while selectively acting as a fixed blade cutter, roller-reamer, lateral vibration damper, friction reducer, stabilizer and/or key-seat wiper. The specific function is dependent on wellbore conditions and is passively activated or engaged during operation. The CRS was successfully field-tested in a middle east field late 2018. Offset well data were used to validate the effectiveness of the tool and provide recommendations for future development.
An offset well was used as a benchmark for comparison to characterize CRS performance. The CRS replaced the stabilizer directly above the measurement while drilling (MWD) tools as part of the BHA used for drilling the interval from 1800 to 2520 meters. When compared to the offset well, the tool had no negative effect on trajectory or dogleg severity. Tight spots required significant back-reaming in the offset well during pull-out-of-hole (POOH). Using the CRS saved 63 hours of rig time when POOH due to the tool’s effective tight spot cutting capability. High torque fluctuations ranging between 2 to 13 klbs-ft were observed in the offset well while drilling formations mainly composed of sticky claystone and limestone. The resulting poor wellbore quality rendered significant logging challenges. The CRS’s ability to damp lateral vibration while engaging in its reaming function resulted in the mitigation of these challenges. Another innovative feature of the CRS’s reaming function is the complete elimination of cutter loss risk. The CRS body is, by far, the industry’s largest area bearing mounted reaming structure and its concentric design eliminates the possibility of it being lost in the hole. The CRS body rotates in response to lateral vibration and drill string whirl when in a vertical or deviated wellbore, effectively contributing to the damping of both vibration modes. The body acts as friction reducer at high deviations. The rotating body also translates on the tool mandrel when faced with a tight spot or pack-off. This translation is opposed by a unique spring assembly that can deliver full top drive torque to the body to cut through the formation.
Al-Zahrani, Talal (Saudi Aramco) | Soliman, Mohamed Ahmed (Saudi Aramco) | Salu, Shamusideen (Saudi Aramco) | Ansari, Nisar (Saudi Aramco) | Al-Shuhail, Khalaf (Saudi Aramco) | Al-Otaibi, Majed (Saudi Aramco)
This paper highlights several opportunities to maximize the total crude oil yield of typical Gas Oil Separation Plants (GOSP's), gas handling and crude oil stabilization systems. This can be achieved for existing facilities by optimizing operating parameters without capital cost or plant modification. Maximizing GOSP's yield (oil recovery) has many advantages such as revenue generation, reducing energy requirements of associated gas handling, mitigating export gas transportation challenges as well as reducing capital cost for new facilities.
Throughout three case studies, this paper demonstrates the impact of operating parameters change in reducing GOSP's total oil shrinkage:
Case Study-1: Pressure let-down optimization of multistage separation
Case Study-2: Temperature optimization of compressors after-coolers
Case Study-3: Temperature optimization of crude stabilization
The analysis was performed for each case study utilizing HYSYS process simulation to establish the optimum operating window for the subject process area. The theoretical results were advanced by conducted field trials under governing operating procedures to validate the conclusion and further explore the benefits as well as the potential challenges of these opportunities.
In case study 1, for high GOR GOSP where more than 3 stages of pressure letdown are required, pressure optimization of the intermediate and low pressure gas/oil separation stages achieved an oil output increase of 3.5 MBD for the same base rate (500 MBD) with dropping gas compression power requirement by 10 MW.
In case study 2, for GOSP's where steady-state hydrocarbon condensate recovered from compressors after coolers knock-out drums is spiked into main Light crude production, optimizing air coolers operating conditions result in a gain of up to 2 MBD in export oil for the same base rate (200 MBD). Moreover, 50% drop in export gas water load can be achieved which helps mitigating pipeline corrosion challenges in gas transportation given the unavailability of a gas dehydration system in the facility.
In case study 3, optimizing inlet temperature of light crude stabilizer enhanced column stripping capability and enabled meeting the required H2S and vapor pressure specification with minimum hydrocarbon liquids losses. A Reduction of 20 °F in inlet temperature resulted in savings of up to 2 MBD stock tank crude for the same base rate of 500 MBD in the expense of reboiler's duty.
Government of India has set an ambitious target of reducing hydrocarbon import. Increasing oil & gas production is one of the measures by which oil & gas import dependency can be reduced. Despite relatively low crude prices globally, substantial E&P activities have been carried out in the country in the last decade, which has witnessed an exponential increase in exploration of oil and gas reserves. Many new fields were discovered during this exploration campaign out of which, few are potential traps containing hydrocarbons. Kutch and Saurashtra Basin off Gujarat coast is one of the exploration fields that involves trap drilling to explore reservoir sands below. Recently for the very first time, in a decade, oil reserves have been discovered in prospective sedimentary basin of Saurashtra. (DGH India Outlook, 2017-18)
Drilling in this basin is characterized by slow rate of penetration (ROP), frequent bit trips, drill string failure, and high well cost. The 12 1/4-in section in this offshore block typically drills through very hard, abrasive and thick layers of Basaltic formation (known as Deccan Trap) with unconfined compressive strength (UCS) between 18-42 kpsi. Conventional polycrystalline diamond compact (PDC) bits and roller cone (RC) bits faced extreme cutting structure damage and delivered poor ROPs in this section. In this paper, challenges of drilling approximately 2,200 m of hard and abrasive Deccan Trap in the 12.25-in section is discussed along with a proposed solution of hybrid bit design by combining conical (CDE) and ridged (RDE) diamond elements.
Two new hybrid 8-bladed 16-mm bit were specifically designed for this application. The first bit drilled an interval of 952m with an average ROP of 1.9m/hr and the second bit drilled an interval of 960m with an average ROP of 1.83m/hr. Both the bits came out of the hole in good condition, thereby delivering a benchmark performance in drilling this challenging section. The runs resulted in 40% reduction in cost/meter for this section and saved 36 offshore days for the customer.
Bailey, Jeffrey R. (ExxonMobil Upstream Integrated Solutions) | Lathi, Harshit (ExxonMobil Services and Technology Private Limited) | Prim, Matthew T. (Abu Dhabi National Oil Company) | Carson, Andrew D. (ExxonMobil Upstream Integrated Solutions) | Tenny, Matthew J. (ExxonMobil Upstream Integrated Solutions) | Payette, Gregory S. (ExxonMobil Upstream Integrated Solutions)
Lateral vibration modeling of certain BHA (bottomhole assembly) designs has shown great sensitivity to the proximity of stabilizer blades. This paper will explore the nature of the vibrational dysfunction that we call BHA chatter. A frequency-domain model that has been field-proven shows how this dysfunction occurs, its rotary speed dependence, and mitigation methods and results.
A frequency-domain BHA lateral vibration model will be used to illustrate the role of the nodal point constraint in the determination of the dynamic side forces acting at stabilizer and LWD tool blade borehole contacts. These contact forces may be strong functions of rotary speed and BHA contact spacing, especially if the spacing is close.
The relationship between the dynamic contact forces and vibration index model results will be described in relation to the solution to the lateral vibration model. Examination of the dynamic contact side forces associated with these vibration indices reveals the nature of the dysfunction that the indices represent.
The contact forces that push a stabilizer blade to be constrained within a borehole include both static and dynamic components. The static forces are well understood. However, the dynamic forces are difficult to visualize as they are generated by the BHA in motion, and a well-formulated dynamic model is required to evaluate these forces.
Dynamic dysfunction at a particular location along the BHA is revealed by examining the underlying states of a dynamic model. Charts of the dynamic contact side force quantify the amount of dysfunction. Vibration indices comprising the integrated, length-averaged bending strain energy provide a good summary of the overall BHA response that is particularly useful in BHA design investigations, but it is the dynamics of the individual contact points that drive the dynamic response of the model.
Examples of field BHA designs illustrate both good and bad drilling results, generally in agreement with expectations based on the modeling. The literature is full of references to the whirl mode of lateral vibrations. This is commonly accepted. Chatter is a different mode that occurs primarily in response to the spacing of blade contacts. It is difficult for two blades that are close together to simultaneously serve as nodal points. A lateral vibration wave propagating along the BHA may generate alternating wall contact at the two blades, causing a dynamic chatter dysfunction.
Rong, Xufeng (China University of Petroleum, East China) | Wang, Yanling (China University of Petroleum, East China) | Forson, Kobina (China University of Petroleum, East China) | Guo, Baoyu (Drilling Technology Research Institute of SINOPEC Shengli Oilfield Service Corporation, Dongying) | Liu, Junyi (Drilling Technology Research Institute of SINOPEC Shengli Oilfield Service Corporation, Dongying) | Wei, Mingzhen (Missouri University of Science and Technology)
In traditional production environments, clay expansion in the near wellbore area may hinder drilling and completion operations. However, most of the above stabilizers cannot meet the actual requirement because the general clay stabilizer cannot migrate through small voids, and can also cause damage to the environment and be very expensive. Herein the behavior of nanoparticles in stabilizing clay particles and the condition for reducing the clay swelling and reservoir damage are investigated.
The adsorption characteristics of nanoparticles on the core surface were studied by adsorption experiments and SEM. Displacement experiments of cores was conducted to discuss the migration behavior of nanoparticle inhibitors. In addition, the Malvern Zetasizer light reflectometer was employed to measure the electrokinetic potential of nanoparticles. To obtain a nanoparticle dispersion system, the dynamic dispersion measurement information of nanoparticle size distribution was collected. In the stability, by controlling the temperature, pH, pressure and other factors, the effects of these factors on the stability of the clay are investigated to obtain the mechanism of action of the nanoparticles.
The core piece was immersed in 1g/L nano-liquid. After adsorption for a period of time, it was observed by SEM that the hydrophobic nanoparticles could form an adsorption layer on the core surface and show a strong hydrophobicity. The nano-electromotive potential is stable at +38.2mV and −36.0mV, indicating that the dispersion is very stable. The dynamic dispersion measurement surface size of nanoparticle dispersion is much smaller than the typical pore and pore channel size in most reservoirs. The microparticles are dispersed and injected through a filter device with a pore size of 200 nm and all of them are dispersed through the core. There is no residue in the filter device, thereby achieving effective migration in the core. It can be concluded that the adsorption effect is stronger under alkaline conditions when the adsorption amount is only reduced by 10% at 950 °C. This is not affected by the pressure factor and also the adsorption effect is stable.
The action of mechanism between nano-silicone material and clay is obtained, and different factors are investigated to find out the prospect of nanoparticles in improving clay stability and reducing the reservoir damage.
Downhole tool failures induced by drill string vibrations was one of the leading causes of nonproductive time in a deep exploratory field in southern Iraq. To improve drilling efficiency, it was paramount to understand the primary source of potential drilling dysfunction before commencing field development phase. To overcome the challenge, a finite element analysis (FEA) study was developed to simulate the drillstring transient dynamic behavior from bit back to surface. The model has been utilized to quantify the potential vibration, contact force, torque, displacement and other high-interest parameters of every drillstring component in the wellbore. To fully exploit the modeling algorithms, it is required to input a comprehensive dataset including mechanical rock properties, cutting structure design, bit drive mechanism, drillstring physical characteristics, 3D well profile and expected drilling parameters.