Underbalanced Drilling Technology Research Articles

UNDERBALANCED DRILLING TECHNOLOGY: BENEFITS, LIMITATIONS, AND CASE STUDIES

The petroleum industry is facing challenging circumstances, including expensive and complex exploration, and the extraction of most hydrocarbons from depleted or lower quality reservoirs. Moreover, current oil prices are at a peak, compelling the industry to re-evaluate its methods and technologies to improve recovery and cut costs. Adopting new technologies, specifically Underbalanced Drilling Technology (UBD), is viewed as crucial for increasing reserves, boosting recovery, reducing expenses, and augmenting revenue. The process of Underbalanced drilling involves intentionally reducing the density of drilling fluid to create lower hydrostatic pressure in the wellbore than the pore pressure in the formation. This technique allows the production of reservoir fluids while drilling, leading to several benefits such as discovering new zones, minimizing formation damage, and increasing well drainage area, which can ultimately increase reserves. However, it is important to note that UBD is not a one-size-fits-all solution and should be planned and executed with caution to avoid over-application or failure, depending on the characteristics of the field, wells, or drilling issues. Keywords: Underbalanced drilling, depleted, technology, hydrocarbons.

Analysis of wellbore stability of gas underbalanced drilling technology

Gas underbalanced drilling technology has the advantages of high ROP and little damage to oil and gas reservoirs. In recent years, it has been widely used in the exploration and development of oil and gas fields in China. Under normal air drilling conditions, the pore pressure is basically zero, so it is necessary to establish the wellbore stability model under the condition of zero pore pressure to provide theoretical support for the wellbore stability analysis of air drilling. However, gas underbalanced drilling also has wellbore instability, more sand deposition at the bottom of the well, and even the malignant accident of sticking. Firstly, through the analysis of the traditional wellbore stability model, the influence of pore pressure is removed, and the wellbore stability model suitable for air drilling is obtained. At the same time, it is proposed that the sand deposition is mainly caused by the collapse material when the collapse ellipse is formed on the shaft wall, and the formation of the collapse ellipse is conducive to maintaining the stability of the shaft wall. For large and medium-sized gravel layers, the influence of cementation strength on wellbore stability should be considered.

Flow Characteristics of UBD Applied to Gas Reservoirs

Underbalanced drilling technology implemented in high pressure and low permeability gas reservoirs can better protect gas formation from drilling fluid damage, and can improve the drilling speed, but gas invade into the wellhole from the formation by the underbalanced pressure will make the borehole flow presented two-phase flow state. The gas phase compactness and slippage effect will increase the drilling of well control difficulty. In order to ensure the invaded gas is not appear violent slippage and rapid inflation, study the two-phase flow law is necessary to determine the size of the applied well backpressure, applying process of gas distribution law in borehole, and the bottom hole pressure, for the reasonable design of drilling fluid density, well backpressure design and the equipment selection. This paper applies the numerical difference method to two-phase flow one-dimensional equations were solved. Combined with an example of drilling, the gas void fraction distribution, migration and bottom-hole pressure change law is given, which provides theoretical basis for low permeability gas reservoirs in underbalanced pressure drilling borehole designing.

Numerical Study of a Flow Field Near the Bit for a Coiled-Tubing Partial Underbalanced Drilling Method

A new drilling method called coiled-tubing partial underbalanced drilling (CT-PUBD) was proposed in this paper. The method is not only able to enhance rate of penetration (ROP) just like the conventional underbalanced drilling technology but can also maintain borehole stability in the upper formation. In the new method, the wellbore pressure system is divided into two parts by a packer: (1) normal pressure system in the upper formation used to balance formation pressure and maintain borehole stability and (2) an underbalanced pressure system in the annulus near the bit used to enhance ROP. Because the pressure system and the circulation system are different, the cuttings transportation process of the method is different from the conventional way. Therefore, it is essential to study how to carry cuttings away efficiently. The flow field and cuttings distribution in the annulus near the bit were analyzed by computational fluid dynamic (CFD) methods. Cuttings transportation trajectory, velocity distribution, and cuttings concentration distribution were obtained under different holes’ parameters of the backflow device (including holes number, diameter, distance, and angle) and different drilling fluid viscosities. The results show that these parameters all have influence on cuttings carrying efficiency, and the most influential parameters are viscosity, angle, and diameter. According to the result of an orthogonal test, a suitable combination of the holes’ parameters was obtained. In the combination, the value of holes number, diameter, distance, and angle is 4, 50 mm, 300 mm, and 120 deg, respectively. This paper provides a theoretical basis for an optimization design of the new method.

Pressure Profile Estimation through CFD in UBD Operation Considering with Influx to Wellbore

Nowadays, UnderBalanced Drilling (UBD) technology is widely applicable in the petroleum industry due to its advantages to an overbalanced drilling operation. UBD success depends on maintaining the drilling fluid circulating pressure below the reservoir pore pressure during operations. One of the main prerequisites of a successful UBD operation is the correct estimation of the pressure profile. In this investigation, the pressure profile was obtained with consideration of the influx to the wellbore. A spreadsheet was developed to obtain the pressure profile using an analytical solution for aerated mud in UBD operation. Moreover, a numerical simulation was employed to simulate the three-phase flow in annulus through the UBD operation and the transient Eulerian model flow via the turbulence k-e model. The effects of solid particle size and rotation of the inner pipe were considered on the pressure drop. It was observed that pressure drop was significantly increased with increasing solid particle size while it remained almost constant with increasing of the inner pipe rotation. The analytical and numerical results were compared with published experimental results and showed a good agreement.

Technology Focus: Drilling Technology and Rigs (February 2018)

Technology Focus When considering the most significant aspects of new drilling technology to highlight for SPE readers, the latest downhole tools, rig design, and operational procedures often make the headlines. This year, however, a case can be made that the most profound advancements exceed anything achievable with new tools, procedures, or machines. On 29 November, the San Antonio Business Journal reported a major oil company had sold a nearby data center to a West Coast cloud-computing giant in a deal estimated at $100 million. The next day, the companies executed a strategic contract to partner and further implement digitization of upstream assets in a cloud-computing environment. The oil company executive involved said, “We have started digitizing our oil fields but want to accelerate deployment of new technologies that position us to increase revenues, lower costs, and improve safety and reliability of our operations.” Far from an isolated event, this case is but one example of an overall trend revolutionizing our industry. Perhaps this is the dominant technology evolution transforming our landscape today. Because drilling and well construction typically involve the majority of the cost and risk for upstream projects, this new revolution is inevitably the game changer for overall health, safety, and environment; efficiency; and financial performance on wells. Phrases such as “dawn of the new age of the oil and gas industry” and “the fourth industrial revolution” echoed through halls of SPE events in 2017 and into the new year, with rapid advancements in big-data management, digital connectivity, and high-performance computing (paper OTC 27638). Exciting developments in new downhole tools, fluids, and rig design continue to advance, with gains in safety and efficiency being multiplied by this transformation. The new revolution is also occurring in parallel with accelerated applications of managed-pressure- and underbalanced-drilling technology. The authors of highlighted paper SPE 185283 suggest the benefits of the technique collectively categorized as closed-loop drilling and the new drilling convention are so numerous that, indeed, all future rig operations should be configured as such. Concurrent with these trends toward increased data acquisition, data analysis, and remote control, automation of rig functionality continues as a primary focus and area of great potential across operator, rig-contractor, and equipment-supplier boundaries. The 3-year industry downturn persisting through 2017 brought an unprecedented purging of paradigms. But perhaps the extreme pressure to reduce costs and add value has indeed forced the innovation and acceleration being realized today during this new revolution. Recommended additional reading at OnePetro: www.onepetro.org. OTC 27638 The Dawn of the New Age of the Industrial Internet and How It Can Radically Transform the Offshore Oil and Gas Industry by Partha Sharma, DNV GL, et al. SPE/IADC 184695 Development to Delivery—A Collaborative Approach to Implementing Drilling Automation by Riaz Israel, BP, et al. SPE 187477 Latest Drilling Techniques Applied to Coring Operations of a Complex Subsurface Geology in WCSB Led to Operational Success and Cost Savings While Setting a Record in North America by Ali Hooshmandkoochi, Seven Generations Energy, et al. SPE/IADC 184650 The Floating Factory Concept: Engineering Efficiencies Up Front To Reduce Deepwater-Well-Delivery Cost by James Hebert, Diamond Offshore

Research on Rapid Identification and Evaluation Technology for Gas Formation during Underbalanced Drilling

The underbalanced drilling (UBD) technology has been widely implemented due to its advantages in drilling efficiency improvement and cost reduction. However, this advanced technology requires very special equipment and operational mechanism, which raises multiple challenges to traditional well logging techniques. In this study, a real-time logging system (MWD/LWD and mud logging) was developed and utilized during underbalanced drilling, to quickly identify and evaluate gas formation. This advanced system enables fast detection of gas formation and determining the formation type while drilling, by monitoring the changes in gas production. This real-time logging system provides a powerful technical support to the gas reservoir drilling and development. A case study has clearly shown that the interpretation and evaluation results based on the real-time logging data agree well with the results of conventional well logging. Therefore, this advanced real-time logging technique can be utilized as an effective guidance for field operation.

Risk analysis of deepwater drilling operations using Bayesian network

Deepwater drilling is one of the high-risk operations in the oil and gas sector due to large uncertainties and extreme operating conditions. In the last few decades Managed Pressure Drilling Operations (MPD) and Underbalanced Drilling (UBD) have become increasingly used as alternatives to conventional drilling operations such as Overbalanced Drilling (OVD) technology. These newer techniques provide several advantages however the blowout risk during these operations is still not fully understood. Blowout is regarded as one of the most catastrophic events in offshore drilling operations; therefore implementation and maintenance of safety measures is essential to maintain risk below the acceptance criteria. This study is aimed at applying the Bayesian Network (BN) to conduct a dynamic safety analysis of deepwater MPD and UBD operations. It investigates different risk factors associated with MPD and UBD technologies, which could lead to a blowout accident. Blowout accident scenarios are investigated and the BNs are developed for MPD and UBD technologies in order to predict the probability of blowout occurrence. The main objective of this paper is to understand MPD and UBD technologies, to identify hazardous events during MPD and UBD operations, to perform failure analysis (modelling) of blowout events and to evaluate plus compare risk. Importance factor analysis in drilling operations is performed to assess contribution of each root cause to the potential accident; the results show that UBD has a higher occurrence probability of kick and blowout compared to MPD technology. The Rotating Control Devices (RCD) failure in MPD technology and increase in flow-through annulus in UBD technology are the most critical situations for kick and blowout.

Daqing Oilfield Liquid Phase Underbalanced Drilling Improving Drilling Speed Evaluation Method

Factors affecting the drilling speed are very complex, such as formation factor (layers lithology, depth, porosity and reservoir pressure), fluid density, drilling parameters (bit pressure and speed), drill types, etc. Although liquid phase underbalanced drilling technology is to increase the penetration rate and shorten the drilling cycle, there is no evaluation model currently, so we cannot evaluate which factors can have a greater impact on speed. Based on the establishment of equivalent density and improvement of ROP (Rate of Penetration) calculation model, this paper is about the application of underbalanced drilling technology to improve drilling speed multiple sizes.

Research and Application of Recyclable Nitrogen Foam Horizontal Well Drilling Technology in the Daniudi Gas Field

AbstractThe Daniudi gas field is typically rich in ultra‐low permeability gas reservoirs in China, but its development is difficult. In this paper, pilot implementation of underbalanced horizontal well drilling technology was used in the H1 gas reservoir to develop the proved reserves effectively. Owing to the limitations of drilling technology and environmental protection, the recyclable nitrogen‐foam was ultimately chosen as a circulating medium. Through theoretical analysis and extensive laboratory tests, the optimal foaming agent composed of α‐olefin sulfonate and coco amine oxide was selected among six anionic surfactants/zwitterionic surfactants systems. The developed recyclable nitrogen‐foam has high salt resistance, temperature resistance and cycle performance, but weaker oil resistance. After the recyclable nitrogen‐foam horizontal well drilling technology was used in the H1 gas reservoir, the average rate of penetration of horizontal section increased by 118 %, ignition could be achieved during drilling and natural gas was of great potential for production. It was the first time to increase natural gas production capacity in the H1 gas reservoir using recyclable nitrogen‐foam horizontal well drilling technology. Successful application of this technology provides technical reserves for the effective development of the H1 gas reservoir.

Underbalanced drilling technology with air injection connector

Underbalanced drilling technology has been extended deeply into every corner of the industrial productions and processes. In particular, the technology has a wide range of applications in oil and gas industries for the product design, manufacturing and construction process. In this work, a new air injection connector system has been developed for underbalanced drilling. The system development includes five key issues: original design, manufacturing control, experimental method, on-spot drilling design, and field work point control. The air injection connector system plays an important role and can significantly reduce potential losses during the drilling process.

Cuttings Transport Models and Experimental Visualization of Underbalanced Horizontal Drilling

Aerated underbalanced horizontal drilling technology has become the focus of the drilling industry at home and abroad, and one of the engineering core issues is the horizontal borehole cleaning. Therefore, calculating the minimum injection volume of gas and liquid accurately is essential for the construction in aerated underbalanced horizontal drilling. This paper establishes a physical model of carrying cuttings and borehole cleaning in wellbore of horizontal well and a critical transport mathematical model according to gas-liquid-solid flow mechanism and large plane dunes particle transport theory.

Managed Pressure Drilling 101: Moving Beyond “It’s Always Been Done That Way"

Tech 101 - The basics of managed pressure drilling. In his book The Nature of Technology, W. Brian Arthur remarked, “The story of this century will be about the clash between what technology offers and what we feel comfortable with.” Although Arthur meant this in technology’s general sense, the same can be said about the clash between underbalanced drilling (UBD) and managed pressure drilling (MPD). The International Association of Drilling Contractors (IADC) defines UBD as follows: A drilling activity employing appropriate equipment and controls where the pressure exerted in the wellbore is intentionally less than the pore pressure in any part of the exposed formations with the intention of bringing formation fluids to the surface. While the benefits of UBD technology include reservoir damage prevention and increases in production and rate of penetration, users can experience discomfort—mainly from operational and safety standpoints, especially offshore—because the well continuously flows to surface while drilling. It can also be expensive, requiring more complex modeling and prediction of compressible drilling fluids behavior during operation. Furthermore, it is not always possible to maintain a continuously underbalanced condition and, since there is no filter cake in the wellbore, any period of overbalance might cause severe damage to the unprotected formation.

Preliminary Study on Air Injection in Annuli to Manage Pressure during Cementing

Along with the development of low permeability reservoirs, underbalanced drilling technology is applied more and more widely. During the cementing operation of underbalanced drilling wells, cementing liquid can flow into the reservoir more easily for the absence of the mud cake, which certainly weakens the reservoir protection advantage of underbalanced drilling. Based on the methods of underbalanced drilling and managed pressure drilling, a new method of cement technology, Balanced Pressure Cementing Technology by Air Injection in Annuli, was put forward. The calculation models of the maximum depth of injection point and the maximum start-up pressure were built. Considering the power limitation of the pump, valves of gas lift were introduced and the calculation method of valve location was developed. This technology could effectively control the annulus pressure of wellbore, assure the cementing quality and protect the hydrocarbon reservoir, thus reduces the exploration and development cost.

Underbalanced Drilling of a Horizontal Well in Depleted Reservoir: A Wellbore-Stability Perspective

Summary The need to reduce formation damage and to avoid differential sticking and lost circulation in depleted reservoirs favors the use of underbalanced-drilling (UBD) technology. In highly depleted reservoirs, the pore pressure can be very low, necessitating the use of extremely low-density fluid to achieve an equivalent circulating density (ECD) below the pore pressure. In such situations, the stress redistribution around the wellbore has to be supported mainly by the rock matrix, and limited support that is provided by the mud pressure. Therefore, UBD can dramatically increase the risk of wellbore instability. From literature review, it was found that the techniques and methodologies to carry out wellbore-stability analysis on UBD of horizontal wells are not well documented. This paper presents a wellbore-stability study that was conducted to evaluate the feasibility of using UBD technology to drill a horizontal well in a highly depleted reservoir in Libya. The study started with geomechanical laboratory tests and mechanical Earth Model (MEM) construction to evaluate the in-situ stresses, pore pressure, and mechanical properties of the formations likely to be encountered during the planned UBD campaign. Wellbore-stability analysis was subsequently conducted for the planned horizontal well to be drilled underbalanced using a new practical approach. The analysis revealed a high probability of extensive and severe breakout within the weak zones if penetrated underbalanced and the potential for massive wellbore collapse. Under the guidance of this study, the well plan and drilling designs were amended to minimize drilling risk.

Well Intervention and Control: Offshore Applications of Underbalanced-Drilling Technology

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 79854, "Well-Control Considerations - Offshore Applications of Underbalanced-Drilling Technology," by Don M. Hannegan, SPE, Weatherford Drilling and Intervention Services, and Glen Wanzer, U. of Oklahoma, prepared for the 2003 SPE/IADC Drilling Conference, Amsterdam, 19-21 February.

Modeling of Transient Cuttings Transport in Underbalanced Drilling (UBD)

Summary Underbalanced drilling (UBD) holds several important advantages over conventional drilling technology. These include minimization of formation damage, faster penetration rate, and ability for evaluation of reservoir productivity during the drilling process. As UBD technology matures, it has also been used more and more in different applications. However, many aspects of UBD technology remain poorly understood. The model presented in this paper seeks to understand the mechanisms involved in the transport of cuttings in UBD. The model simulates the transport of drill cuttings in an annulus of arbitrary eccentricity and includes a wide range of transport phenomena, including cuttings deposition and resuspension, formation, and movement of cuttings bed. The model consists of conservation equations for the fluid and cuttings components in the suspension and the cuttings deposit bed. Interaction between the suspension and the cuttings deposit bed, and between the fluid and cuttings components in the suspension, are incorporated. Solution of the model determines the distribution of fluid and cuttings concentration, velocity, fluid pressure, and velocity profile of cuttings deposit bed at different times. The model is used to determine the critical transport velocity for different hydrodynamic conditions. Results from the model agree quite closely, qualitatively, with experimental data obtained from a cuttings transport flow loop at the Technology Research Center of the Japan Natl. Oil Corp. (TRC/JNOC)'s Kashiwazaki Test Field in Japan. These results show the importance of slippage in the formation of the cuttings deposit bed. The model is useful in evaluating the minimum flow rate for effective cuttings removal in UBD.

Wellbore Stability Simulations for Underbalanced Drilling Operations in Highly Depleted Reservoirs

Summary The need to increase productivity and to reduce drilling formation damage favors the use of underbalanced drilling technology. The main idea is to drill with equivalent circulating densities (ECD) that are less than the formation pore pressure and to avoid contact between the drilling fluid and the formation. In highly depleted reservoirs, pore pressures can be very low. Therefore, extremely low-density fluids, such as foams, are used to achieve circulating densities lower than the pore pressure. In such cases, the induced modification of the in-situ stresses has to be supported mainly by the rock, with little contribution from the drilling fluid pressure. In that sense, the application of underbalanced drilling depends on the mechanical stability of the drilled formation, among other factors. In general, poorly consolidated, depleted formations are not suited for that technology. This paper presents the wellbore stability simulation performed to establish the feasibility of using underbalanced drilling in highly depleted reservoirs in western Venezuela. The in-situ stress field and the mechanical properties of the formation were obtained. Pore pressure as low as 800 psi at 5,500 ft (2.7 lb/gal equivalent fluid density) was measured. The finite difference method and an elastoplastic constitutive model was used to obtain the new stress, deformation, and pore pressure distribution. The undrained condition (immediately after the wellbore is drilled) as well as the drained condition were analyzed. The analysis showed that horizontal wells could be drilled in an underbalanced condition with low instability risk. Following the recommendations, four horizontal wells were drilled in underbalanced conditions. Values as low as 2.0 lb/gal ECD were used to drill the wells, and no wellbore instability problems were reported. Production tests showed an enormous increase in the well productivity index in comparison with conventional overbalanced drilling.

Using Underbalanced Drilling to Reduce Invasive Formation Damage and Improve Well Productivity-An Update

Abstract Underbalanced drilling (UBD) is becoming increasingly used as a technique to reduce significant invasive formation damage in vertical and horizontal wells to improve production rates of oil and gas, and enhance injectivity in gas and water injection situations. UBD may be a technically demanding procedure to execute in certain reservoirs and much of the benefit with respect to mitigation of formation damage may be compromised if the underbalanced drilling operation is not screened, designed and conducted in an appropriate fashion. This paper reviews common formation damage mechanisms which may occur in reservoirs and how, in certain situations, these types of damage may be reduced or eliminated through the appropriate use of underbalanced drilling technology. Various situations in which underbalanced drilling technology may result in potential significant formation damage are also discussed. Introduction Underbalanced drilling is utilized worldwide for the drilling of horizontally and vertically oriented wells to increase rates of penetration, reduce invasive formation damage and reduce problems with drilling due to lost circulation and differential sticking. Many successful descriptions of underbalanced drilling are present in the literature(1–8). However, underbalanced drilling is not a panacea for all formation damage problems in that inappropriately designed underbalanced drilling jobs may actually result in more formation damage than if a well-designed and contemplated overbalanced job had been used in the same circumstances. This paper reviews some of the technology in use at the present time in underbalanced drilling, and illustrates some of the points which operators should be aware of before embarking on an underbalanced drilling operation. What Is Underbalanced Drilling (UBD)? A rigorous definition of UBD is a condition where the circulating pressure of the drilling fluid in contact with the formation is less than the effective pore pressure in the adjacent matrix. The desirable course of action is to have this occur along the entire exposed section of the productive pay of the reservoir, resulting in an inflow of oil, water or gas (which may be contained in the matrix) into the wellbore. The produced fluids are returned to the surface along with the circulating drilling fluid. A number of descriptions of UBD exist in the literature. They can be described as follows: Overbalanced Drilling A situation in which the equivalent circulating density of the drilling mud is sufficient that, at bottomhole conditions, the drilling fluid pressure is greater than the formation pressure, resulting in an effectively "killed" state (where no inflow of formation of fluids occurs). This has been the most common technique utilized to drill wells in the past and is still the dominant technology currently used to drill many wells. Low Head Drilling Low head drilling refers to a situation where an overbalance pressure condition, similar to that described above, is maintained but with the use of lower density oil-based fluids or possibly gasified fluids to reduce the magnitude of the overbalance pressure exerted on the formation. The prime motivation is to reduce formation damage and the potential for severe invasive losses and to increase ROP. Low head drilling is still classified as a form of overbalanced drilling.

アンダーバランス掘削技術 ２

アンダーバランス掘削技術 ２