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.
Zheng, Ma Jia (Southwest petroleum University) | Liu, Xin (Schlumberger Technology Services, Chengdu, Ltd) | Zhao, Jian Ping (PetroChina Southwest Oil and Gas Field Company) | Qiu, Xun Xi (Sichuan Shale Gas Exploration and Development Company Ltd) | Fang, Jian (CCDC Geological Exploration & Development Research Institute) | Wang, Xiong Fei (Schlumberger Technology Services, Chengdu, Ltd) | Zhao, Jing Kai (Schlumberger Technology Services, Chengdu, Ltd) | Geng, Gan (Schlumberger Technology Services, Chengdu, Ltd)
The Sichuan Basin is the major target for shale gas exploration in China because of its rich gas stored in unexploited black shale with multiple bed series. National Shale Gas Exploitation Areas have been established since 2012, the proved geological shale gas reserves is 9210×108 m3 and 90.25×108m3 annually output has been achieved by the end of 2017.
The operating Sichuan Basin shale gas area located in the major compression tectonic experienced multiple geological structure movements in Earth history, showing characteristics of high steep structure with faults greatly developed. It's proven that the key factors in exploiting these targets are well acknowledged by the efforts to land and expose the lateral within the sweet zone. To successfully place lateral in reservoirs from geological perspective must overcome challenges of high uncertainty structure identification to make soft landing and maximize horizontal exposure in the sweet zone.
While it comes to shale gas reservoir, to pave the way for fracture operation and achieve good well completion, the drilling requires a relative gentle well path, keeping well path inclination with limitation, which requires to make azimuth turning to achieve this.
To ensure the optimum placement of the well in sweet zone, the integration of rotary steerable drilling system (RSS) with borehole images measurements in real-time have been implemented with the employment of well placement technique.
The borehole image portrays structural profile while drilling whilst the rotary steerable drilling system provides accurate trajectory control. With the help of borehole image and proactive log correlation, the trajectory can be landed precisely into desired best quality reservoir, although the formation dip and actual target depth become much different with geological prognosis. During the lateral section, the trajectory was also controlled effectively in the high-quality reservoir despite of structural variation and reservoir property change. Through use of Fit-For-Purpose solution it effectively improves drilling efficiency and positively impacts well production. These achievements subsequently help to optimize wells deployment plan and wells with longer lateral horizontal section were planned for greater predictable production rate.
Wang, GaoCheng (PetroChina Zhejiang Oilfield Company) | Zhao, Chunduan (Schlumberger) | Liang, Xing (PetroChina Zhejiang Oilfield Company) | Pan, Yuanwei (Schlumberger) | Li, Lin (PetroChina Zhejiang Oilfield Company) | Wang, Lizhi (Schlumberger) | Rui, Yun (PetroChina Zhejiang Oilfield Company) | Li, Qingshan (Schlumberger)
Huangjinba shale gas field is located at the south edge of the Sichuan Basin. It has very complex structures, in situ stresses and natural fracture corridors in comparison to adjacent areas in the Sichuan Basin. In recent drilling campaigns, drilling risks have caused some wells to fail in reaching their planned total depth, eventually failing to deliver cost-effective gas production. In order to mitigate drilling risks, e.g. mud loss, collapse, stuck, hang up, gas kick, effective drilling risk prediction is an urgent challenge to address. Integrating quantitative drilling risk prediction methods with qualitative methods could increase the prediction accuracy and avoid or mitigate the drilling risk during the well deployment stage.
In this project, multiple seismic attributes were used to predict natural fracture distributions which qualitatively indicated the locations where drilling risks were likely occur. Comprehensive geophysical characterization was performed to identify natural fracture zones and patterns, and their mechanisms were validated by analyzing regional geological and tectonic evolution.
Image log data was then integrated into the natural fracture distribution prediction from seismic to build a DFN (Discrete Fracture Network). This combination of the DFN predicted from seismic data plus quantitative image log information allowed improved accuracy in the prediction of drilling risks.
Following this, natural fracture stability was analyzed by building a 3D geomechanics model in order to predict drilling complex qualitatively. A full field 3D geomechanics model was built through integrating seismic, geological structure, log and core data. The 3D geomechanical model includes 3D anisotropic mechanical properties, 3D pore pressure, and the 3D in-situ stress field. Through leveraging measurements from an advanced sonic tool and core data, the anisotropy of the formation was captured at wellbores and propagated to 3D space guided by prestack seismic inversion data. 3D pore pressure prediction was conducted using seismic data and calibrated against pressure measurements, mud logging data, and flowback data. The discrete fracture network model, which represented multi-scale natural fracture systems, was integrated into the 3D geomechanical model during stress modeling to reflect the disturbance on the in-situ stress field by the presence of the natural fracture systems.
From these models, a drilling map which quantitatively indicated the depth where drilling risk such as mud loss, gas kick, etc. occurred was created along the well trajectory.
This paper presents the highlights and innovations in seismic multi-attributes analysis and full-field geomechanics modeling which integrate qualitative and quantitative methods for drilling risk prediction.
This paper provides technical feedback of a successful use of Directional Casing While Drilling (D-CwD), a technique allowing to simultaneously drill and case the hole while following the directional plan. It highlights how substantial gains were realized on Badamyar project in Myanmar, having benefited from the D-CwD technique to optimize the architecture.
The Badamyar development campaign involved the drilling of four horizontal gas wells in conventional offshore environment in Myanmar. Other regional wells had already experienced wellbore issues to get the 13 3/8″ casing vertically to 450m. On Badamyar, drilling directly with the casing allowed to minimize operational exposure to losses and wellbore instability, and to achieve the challenge to get the 13 3/8″ to 800m and 45deg inclination, avoiding the requirement for an additional surface casing.
All four 13 3/8" sections were successfully directionally casing-drilled and cemented in fourteen days within budget duration, which, despite the additional complexity, is comparable to the best performance in the block in the last twenty years. The average Rate of Penetration was 30 m/hr, same as fastest conventional case in the field, without mentioning the huge advantage that when reaching the required depth, the casing is already in the hole. Indeed, once the casing has reached the required depth, drill pipe is run inside the casing to unlatch and recover the directional BHA, and pull it back to surface, leaving the casing in place ready for the cement job. While conventionally, casing still needs to be run with associated time and risks (losses, wellbore stability, stuck casing, accidental side-track, etc…).
This Directional-CwD was a new concept to most of the teams involved: Operator, Rig contractor and Tubular Running Services. It required changing the "hundred and thirty years of conventional drill-pipe drilling" mindset. This paper describes the decision making process to switch from conventional to casing-drilling, the preparation phase where risks were identified and mitigated, as well as the excellent operational results.
This paper, by presenting a successful first implementation within a major O&G company, brings to the drilling industry an additional case that the system works, is technically fit-for purpose, cost effective, and has the tremendous potential to replace conventional drilling in several applications. It also highlights some potential limits and opportunities for optimization which should be considered for further development (trajectory constraints, fatigue life and well control).
Jiang, Tongwen (Tarim Oilfield Company, PetroChina) | Zhang, Hui (Tarim Oilfield Company, PetroChina) | Wang, Haiying (Tarim Oilfield Company, PetroChina) | Yin, Guoqing (Tarim Oilfield Company, PetroChina) | Yuan, Fang (Tarim Oilfield Company, PetroChina) | Wang, Zhimin (Tarim Oilfield Company, PetroChina)
The Jurassic fractured sandstone gas reservoir has low permeability and strong heterogeneity in northern Kuqa depression in Tarim Basin. Therefore, the use of highly deviated well will be an effective way to improve efficiency of natural gas development. But the drilling of highly deviated well was faced challenges associated with complex geologic conditions: ① How to optimize the trajectory of highly deviated well to penetrate permeable fractures? ②How ensure the wellbore stability during drilling? ③ How to optimize fracturing stimulation program after drilling?
To demonstrate the feasibility of highly deviated well and optimize its drilling program, an integrate research combined geology, geomechanics and petroleum engineering was conducted. The stress regime, magnitude and orientation were defined by using borehole information, including log data, lab tests, leak off and drilling experience. The distribution characteristics of in-situ stress were described by structural architecture, 3D seismic data and numerical simulation. By analyzing the relation-ship between in-situ stress and development of natural fractures, the key geological factors controlling reservoir quality were further defined. Based on the estimation of stress state acting on natural fractures, the orientation of effective fractures in gas reservoir space was predicted. The wellbore stability was analyzed by considering stress variation, borehole deviation and in-clination orientation. Finally, the reservoir fracability was evaluated by incorporating stress, shear-to-normal stress ratio of fractures, brittleness and fracture toughness.
It is shown that in-situ stress not only affects density and orientation of natural fractures, but also indirectly affects the quality of reservoir by controlling the mechanical behavior of natural fractures. Therefore, the geomechanical model is a useful supplementary geological attribute in gas well planning and wellbore trajectory optimization, and then it is also an important basis for optimization of drilling program and design of fracturing stimulation. Based on this concept, the necessity and feasibility of highly deviated well drilling were proved in Jurassic fractured sandstone reservoir of northern Kuqa depression. Then, two conditions of low in-situ stress magnitude and weak horizontal stress anisotropy were used as supplementary basis for gas well placement optimization. Finally, the wellbore trajectory of highly deviated well was optimized by combining borehole drilling across permeable fractures, wellbore stability and fracturing stimulation post-drilling. The optimized well site and wellbore trajectory effectively minimized cost and risk, while maximizing the well performance.
The first highly deviated well was successfully drilled under complex geologic conditions in Kuqa depression. Its wellbore trajectory was relatively stable and was conducive to fracturing. Theoretical calculations and actual drilling experience were consistent, which indicated that it is feasible to develop natural gas using highly deviated well, and it also proves that the geomechanical approach is effective in optimizing well location and wellbore trajectory in Kuqa depression.
Momot, Fabien (PathControl) | Humbled, François (RMI) | Garbers, Martin (TOTAL SA) | Shabanov, Sergey (TOTAL SA) | Gonsette, Alexandre (RMI) | Sikal, Anas (PathControl) | Cousso, Olivier (TOTAL SA) | Reynaud, Denis (PathControl)
Improvements in measurement while drilling (MWD) and service reliability over the past 25 years has made MWD tools the most cost-effective method for calculating wellbore survey position while drilling. However, with more complex well trajectories required to reach more challenging targets, reducing lateral uncertainty has also become a new challenge.
It is accepted that no geomagnetic model can properly account for the geomagnetic spatial and temporal local complexity for calculating MWD geomagnetic reference values. It is also well known that measuring local geomagnetic reference requires frequent absolute measurements in order to perform QA/QC, and that those absolute measurements could only be done manually so far, and consequently very few magnetic observatories are in operation. Therefore, solutions have been engineered to enhance the geomagnetic reference model with In-Field Referencing (commonly termed as IFR). Then, its combination with Multi-Station Analysis (MSA) correction algorithms has become a common method for addressing and reducing most of the correctable MWD azimuth, survey position error and lateral uncertainty.
Enhanced wellbore positioning could be a real game changer to achieve in-fill wells with high collision avoidance constraints, to develop projects that require high precision to hit the reservoir targets, or those located in specifically difficult areas, from a geomagnetic perspective, such as high latitudes and zones with crustal anomalies.
This paper presents the results of the new temporal magnetic field method "IFR4D" that was successfully used to drill two onshore wells in Argentina. The wells targeted the Vaca Muerta shale play, and demonstrated the ability to improve the wells absolute positioning while reducing the lateral aspect of "ellipse of uncertainty" by a combination of: A unique autonomous, remote real-time observatory developed to monitor and allow corrections for the local geomagnetic vector with frequent absolute control of the local and temporal geomagnetic vector field (Dip, Declination and Field Intensity), and A dedicated MSA algorithm defined to use local and temporal In-Field Referencing (IFR2) data at the position and time for each MWD survey station.
A unique autonomous, remote real-time observatory developed to monitor and allow corrections for the local geomagnetic vector with frequent absolute control of the local and temporal geomagnetic vector field (Dip, Declination and Field Intensity), and
A dedicated MSA algorithm defined to use local and temporal In-Field Referencing (IFR2) data at the position and time for each MWD survey station.
Once installed on location, the autonomous observatory measured all geomagnetic properties (Dip, Declination and Field Intensity) with no personnel onsite for more than one year, delivering a new level of geomagnetic accuracy to use as the standard reference for the life-time of the field. The data from the observatory was then used remotely while drilling to correct and optimize wellbore position and reduce the lateral aspects of the "ellipse of uncertainty" (EOU).