Directional drilling for hydrocarbon exploration has been challenged to become more cost-effective and consistent with fast-growing drilling operations for both offshore and onshore production areas. Autonomous directional drilling provides a solution to these challenges by providing repeatable drilling decisions for accurate well placement, improved borehole quality, and flexibility to adapt smoothly to new technologies for drilling tools and sensors. This work proposes a model predictive control (MPC)-based approach for trajectory tracking in autonomous drilling. Given a well plan, bottomhole assembly (BHA) configuration, and operational drilling parameters, the optimal control problem is formulated to determine steering commands (i.e., tool face and steering ratio) necessary to achieve drilling objectives while satisfying operational constraints. The proposed control method was recently tested and validated during multiple field trials in various drilling basins on two-and three-dimensional (2D and 3D) well plans for both rotary steerable systems (RSS) and mud motors. Multiple curve sections were drilled successfully with automated steering decisions, generating smooth wellbores and maintaining proximity with the given well plan.
In several producing fields throughout the Norwegian continental shelf, operators are facing aging wells with heavily deformed completions that are producing below their potential. In order to find a technical solution to improve production that can be operated through completion deformations, Archer, Archer has pursued a full technical study of existing collapse geometry, axial pipe displacement and reproduced them in full scale 3D models in order to test a newly engineered slim and highly flexible perforating system designed to be conveyed by carbon composite rod with embedded electrical cable.
In March 2018, work began in parallel on two linked projects. We needed first to understand the different profiles and geometries of an inaccessible deformed tubular, in order to reproduce and model the axial displacement on scale. In parallel with the deformation modelling, we needed to engineer with our perforating system manufacturer an interchangeable and flexible perforating system capable of passing through the 3D model deformations.
A complete study of downhole recorded well data from deformed areas was performed to catalogue the different possible shapes and internal diameter reduction of tubing and liner under axial compression. A 3D modelled transparent plastic tubular system has been engineered in order to reproduce the exact downhole dimensions and conditions of known deformed areas. The modelled deformations needed to be robust and long enough to support real downhole tools and fully transparent so we could understand the different toolstring’s behaviorsbehaviours depending on the Bottom Hole Assembly (BHA) set up and shape of the deformation. The deformation testing system has been created as a light weight interchangeable tubular system designed to interlock quickly and easily in various combinations.
In the meantime in the parallel twin project, the initial task was to review the current product portfolio of slim through tubing equipment. The completion with heavy wall liners, intended to minimize the deformation caused by reservoir formation movements, challenged the charges selection that could be fitted into slim perforation systems. Due to the minimum hole size requirement, the gun system was also designed to self-orient to the low side of the casing. The drafting team analyzedanalysed the internal gun system and added a weighted row to assist with gun orientation. The final system to be tested in the modelled deformation is composed of interchangeable swivels, knuckle joints, rollers, and single or multiple shot slim and short guns incorporated with addressable switches.
Over 30 different well deformation shapes have been recreated in order to test and select the best performing flexible perforating system combination, leading to more than 200 documented results. The flexibility and reduced Outer Diameter (OD) of both downhole system and composite carbon rod allows to pass successfully through several heavily deformed tubulars, when every other conventional rigid system have has failed.
The method for modeling of a multilateral well design that is completely independent on the simulation grid and fluid properties is proposed. The method takes into account friction in the lateral branches and crossflow between them. Well parameters, such as trajectory, perforation intervals, roughness and diameter, are directly used to calculate pressure distribution along the wellbore at the current fluid composition and tubing head pressure (THP).
Well connections with grid blocks in a finite volume approximation for dynamic model should be created. The automatic creation of the well connections during dynamic simulation based on specified well trajectory and completion intervals is proposed. The connection factor is suggested to be calculated based on length of completion intersection with the block, trajectory direction and rock properties during the run time. To calculate pressure drop on well track intervals between connections and the well track intervals between top completion and tubing head the well-known correlations are utilized. The correlations are used for the current fluid composition in the wellbore in each connection using information for well trajectory, roughness and diameter.
Such an approach makes it possible to get rid of the use of the tabulated bottomhole pressure (BHP) as a function of tubing head pressure for a number of phase compositions. Such traditional use of phase compositions gives a non-physical response in compositional models, where the component composition of the product varies significantly throughout the life of the field. Usage of real coordinates (x, y, z) for setting well trajectory and perforation intervals, instead of the traditional grid block numbers (i, j, k), allows to calculate layer intersection, connection factors and pressure distribution along wellbore with arbitrary changes in the dynamic model grid, for example, when introducing local grid refinement or dynamic grid and rock properties variation used to describe hydraulic fracturing.
The proposed method is successfully used for modeling of a multilateral well design in dynamic simulation. The results of such dynamic simulation are consistent with the real samples from reservoir.
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 objective of this study was to examine the techniques of selecting logging-while-drilling (LWD) tools for geosteering in unconventional reservoirs by examining the workflows and choices from case studies. When planning a horizontal well one of the most important decisions is choosing the measurement that will be used to steer. Which tool to select depends on the measurement contrast between the target formation and the surrounding formations, target thickness and most importantly what are the project objectives.
Judiciously choosing the correct measurement can help maximizing exposure within the target window and reduce trouble time and sidetracks. Steering within unconventional reservoirs is generally done using the simplest measurements possible, the measurements-while-drilling gamma ray (MWD GR). This is due to cost or lack of perceived need for additional measurements, or because GR gives enough information with the large amount of offset data that exists. We looked at several case studies where tools were selected by analyzing the offset for measurement contrast and forward modeling the planned well trajectory across the zone and exiting the top and base of the target window.
One case was a series of wells in the Olmos sand found in the coastal area of south Texas. The target is a higher-porosity layer within the Olmos “C” sand, which is approximately 10 to 12 ft thick with surrounding rock is that is tighter but will produce if fractured. The project objective was to drill wells to maximize exposure in the high-porosity layer, then hydraulically fracture the reservoir. The offset log data was forward modeled, then the best measurement that would achieve project objectives was chosen and the wells drilled.
The offset data was forward modeled and it showed that because of the symmetrical nature of the target window, an azimuthal measurement was needed. Both azimuthal GR or resistivity would work in this environment, but to distinguish between the tighter formation above and the target with a similar resistivity value a different measurement would be needed to have a unique measurement that could distinguish between the higher density rock above the target and lower density rock below the target, and an imaging density tool was selected to steer the well.
The wells were landed in the target zone using a conventional gamma ray (GR), and then geosteered during the lateral using real-time density images from an LWD tool. The images were used to measure formation dips, both within the target and after the trajectory was forced out of the zone by a subseismic fault. The formation dip was determined to plan the sail angle to allow for getting back in zone most efficiently.
Selecting the proper measurement by careful analysis beforehand allowed the wells to be steered successfully, which led to increased production compared to offset horizontals steered without an azimuthal measurement.
Baheti, Murli Manohar (Cairn Oil & Gas, Vedanta Ltd) | Sinha, Pankaj (Cairn Oil & Gas, Vedanta Ltd) | Prabhakaran, Tushar (Cairn Oil & Gas, Vedanta Ltd) | Paliwal, Kunal (Cairn Oil & Gas, Vedanta Ltd) | Sharma, Anurag (Cairn Oil & Gas, Vedanta Ltd, Brunel) | Doodraj, Sunil (Cairn Oil & Gas, Vedanta Ltd) | Vermani, Sanjeev (Cairn Oil & Gas, Vedanta Ltd)
The paper presents a case study on adopting an economics driven novel approach to directional well planning and drilling a horizontal well in a single well FDP (field development plan) for a marginal field in onshore India. The paper highlights the successful drilling of 8-1/2″ landing production section with DLS > 7 deg/30m followed by the 8-1/2″ horizontal lateral. The feasibility of achieving high DLS well trajectory using basic directional tools and associated hole problems with their mitigations are addressed in the paper.
Low crude price resulted in marginal economics for the above FDP. To improve economics, the capital expenditure had to be minimized (by utilizing existing well pads and production facilities) and maximize oil production (by drilling horizontal wells). Hence, constrained surface locations and fixed subsurface targets resulted in complex well trajectory (DLS>7). The Trajectory was finalized after multiple iterations to ensure that it is meeting requirements of deep set artificial lift, free of collision threats and also meeting the geological objective of placing the well in a thin reservoir with defined GOC and OWC. The final well design included one 12 ¼″ surface section with 9-5/8″ casing and 8-1/2″ production hole with 7″ casing to TD (~1800m MD). The well was initially planned with special RSS tool which could achieve high DLS, but the cost and lead time were the contra-indicators. Hence, the 8-1/2″ hole was planned with two BHAs. The build and land section was planned with motor (1.6 deg bend and rpm limitations) and tricone bit BHA to build from 9 deg to 90 deg inclination with a DLS of 7 deg/30m in 400m closure. The horizontal lateral was planned with RSS BHA and PDC bit including density image LWD for geosteering. To minimize hole sections for cost reduction, the landing and horizontal section was combined in a single hole which increased risk associated with wellbore stability, hole cleaning and casing running. The risks were suitably addressed through in-house geo-mechanics inputs, application of ERD procedures & real time T&D monitoring
With no offset well data (in onshore India) to substantiate the possibility of achieving high DLS trajectory, the motor and tricone bit BHA successfully achieved the desired trajectory with max DLS ~11deg/30m and without any hole problems. The well was successfully landed and placed in the reservoir. The operator gained significant confidence in understanding of drilling high DLS wells without expensive drilling tools
PY-1 is one of the few fields in India producing hydrocarbons from Fractured Basement Reservoir. The field was developed with nine slot unmanned platform with gas exported through a 56 km 4" multiphase pipeline to landfall point at Pillaperumalnallur. Field was put on production in November 2009 with three extended reach wells. The production performance of the field had some surprise and declined earlier than expected. As a result, based on the conclusions drawn from an integrated subsurface study, a two wells reentry campaign to side track wells Mercury and Earth was planned to be executed in Q1 2018. The objectives of this paper are twofold: 1. Review the production performance of a granitic basement gas field and share learnings which may be useful for similar fields being developed elsewhere.
The effects of horizontal well geometry remain debatable in most production modeling works. Most of recent reports fail to mention the effects of well geometries, especially in severe slugging cases. This study presents a qualitative comparison between different well geometries and their impacts in production performance of horizontal wells.
The study utilizes a transient multiphase simulator to mimic the production from a horizontal well over a 12-hour period. The well has a 2-7/8″ ID tubing with TVD of approximately 5000 ft and MD of 10000 ft and maximum inclination angle of 10º within the horizontal section. The trajectories of horizontal section in the well include 5 cases, 5 undulations, hump (one undulation upward), sump (one undulation downward), toe-up and toe-down. These configurations are the representative examples of horizontal wells. A reservoir with a given deliverability equation and several perforation stages is used to provide well inflow. The impacts of reservoir deliverability, GOR, pressure and temperature are studied for all well geometries.
The simulation results offer some valuable insights into the effects of well trajectory on production performance, including borehole pressure profile, liquid holdup, gas and liquid rate variations with time, and cumulative gas and liquid production. At high production rates, severe slugging is not observed, and thus, the well geometry effects are minimized with a consistent production at the surface. However, toe-up configuration exhibits a slightly better performance than the others.
As the productivity and pressure reduces throughout the life of a well, the impacts of well trajectories become clearer. The presence of severe slugs and blockage of perforations near the toes causes a noticeable drop in production. During severe slugging, the pressure profile reveals longer fluctuation cycles, resulting in extreme separator flooding issues. The slugging frequencies are compared among different well geometries. Toe-down case exhibits lower slugging severity. As a result, toe-down well produces the highest cumulative liquid and gas rates. The presence of liquid blockage is observed in lateral and curvature sections. The toe-up and hump configurations exhibit the most severe slugs with minimum cumulative gas and liquid productions. The differences in productions among well trajectories exceed 30% under different well configurations.
With the augmented growth of production from unconventional reservoirs, horizontal well technology has grown in oil and gas industry, yet study of well geometry in production system remains to be limited. This study is a unique effort to optimize well configuration and perforation placement in order to alleviate multiphase flow problems in the wellbore. Providing the practical potential on simulation works, this study provides a predictive guidline to connect well geometry selection and production optimization.
Krishna Godavari Offshore Block has reservoir temperatures of 420 degF and 12,500 psi of bottom hole pressures, field's HPHT rating is a concern moreover other challenges like the wells are complex in terms of depths, profile, high drift, reservoir with heterogeneity, formation pressure variation. The paper discusses challenges during well planning and their execution with adequate methods to successfully drill and case well with less than 15 % NPT.
In harsh environment of KG Basin, HPHT wells encroach on limits of equipment, leaving little margin for error, resulting in increased risk of rapid gas migration, equipment integrity failure, operating limits of tool. The paper discusses use of RSS-Vortex, 200 degC rated MWD tools, NRDPP, modified casing design, reduction in impact of side forces and high torques, optimized bit design, drill pipe cutting tool, reduction of differential sticking to execute the drilling of well within given time. The case study discusses longest 5 7/8" section drilled in an unconventional casing design under HPHT environment in India.
The paper also discusses the unexpected results and observations obtained during execution of program and the lessons learnt from it. Some drilling methods such as first application of RSS-Vortex in a HPHT environment in India has considerably enhanced the ROP by 100% and also significantly reduced casing wear of production casing by 55 %, use of 200 deg C rated MWD tools has increased the robustness of the drilling BHA resulting in minimizing additional BHA trips due to tool failures. The reservoir section drilling has been optimized to 3 bit trips from 9-13 trips done in offset wells. Use of NRDPP's made drilling of high drifted wells easier and maintenance of surface torque within limits had considerably reduced lost production time and ensured safe operation. The improvisation carried out for bit design and casing design has also saved rig days and cost. The new casing design avoids liner tie back which has resulted saving of 7 days of rig time. The use of effective micronized barite OBM system with controlled measures on HTHP fluid loss has maintained good balance between rheology and fluid loss to prevent differential sticking. The downhole tool failure and stick-slip was reduced by 50% by modulating the Variable frequency drive and choosing adequate bit.
These methods and practices require further optimization to enhance the usability. The established methods discussed have created good drilling practices in HPHT environment for KG field and has reduced the drilling NPT levels. Such a huge transformation in reducing the NPT is very significant in HPHT conditions and many of the practices can be standardized for such operations.
Lv, Zuobin (Tianjin Branch of CNOOC Ltd.) | Gao, Hongli (Tianjin Branch of CNOOC Ltd.) | Cheng, Qi (Tianjin Branch of CNOOC Ltd.) | Cheng, Dayong (Tianjin Branch of CNOOC Ltd.) | Meng, Zhiqiang (Tianjin Branch of CNOOC Ltd.)
JZS is an offshore metamorphic rock buried hill oilfield. Both horizontal and vertical velocities of the oil field change very fast. The interval velocity of the buried hill stratum is twice that of the overlying strata, and the top surface of the buried hill fluctuates greatly with a maximum height difference of 300m. In the complex buried hill reservoir, since the current professional seismic software can not realize variable time-depth relationship in horizontal direction, which leads to the error of the trajectory form and position of the horizontal well in time domain, therefore the well trajectory in time domain is not matched with that in depth.
In this paper, a new practical trajectories matching method for buried hill horizontal wells in time domain and in depth is presented. First of all, we carried on the research on the theoretical form of horizontal well trajectory in buried hill in time domain. The research shows that the theoretical trajectory form of a horizontal well in buried hill is consistent with trend of the buried hill top surface morphology. On the basis of theoretical research, by establishing the pseudo time-depth relationship of horizontal well based on measure depth (MD) and seismic reflection two way time (TWT), we realized the accurate characterization of the trajectory form and position of a horizontal well in buried hill in time domain: (1)For normal horizontal well with no more than 90 degrees inclination angle, we can respectively establish the pseudo time-depth relationship of the horizontal well in buried hill segment and in upper segment, and then merge both time-depth relationship data into a whole; (2)For the complex horizontal well with well segment whose inclination angle is more than 90 degrees, we need firstly split the well trajectory into normal well segment and complex segment according to inclination angle, then establish the pseudo time-depth relationship in normal and complex well segments respectively. More specifically, we can split the trajectory into normal trajectory segment with the inclination angle no more than 90 degrees and complex trajectory segment with the inclination angle more than 90 degrees, for normal segment, we can establish pseudo time-depth relationship like the normal horizontal well described earlier, for complex trajectory segment, we need creatively invert the top and bottom of the complex segment to convert inclination angle of the segment to within 90 degrees, and then establish pseudo time-depth relationship of the inverted segment.
Through this method, we can obtain the accurate trajectory form and position of the horizontal well in time domain and it provides a basis for accurate geological modeling based on 3D seismic attributes constrains. The real reservoir performance of JZS buried oilfield in Bohai Bay in China has proved that the 3D geological model based on the new time-depth relationship (MD&TWT) of the horizontal wells is closer to the actual reservoir.