Well Drilling

The fluid pressure, the stress due to the column of the cement in the annulus of oil and gas wells, and the radial pressure exerted on the cement sheath from the surrounding geological layers all affect the integrity of the cement sheath. This paper studies the impact of CO₂-bearing fluids, coupled with the geomechanical alterations within the cement matrix on its integrity. These geochemical and geomechanical alterations within the cement matrix have been coupled to determine the cement lifespan. Two main scenarios including radial cracking and radial compaction, were assumed in order to investigate the behaviour of the cement matrix exposed to CO₂-bearing fluids over long periods. If the radial pressure from the surrounding rocks on the cement matrix overcomes the strength of the degraded layers within the cement matrix, cement failure can be postponed, while on the other hand, high vertical stress on the cement matrix in the absence of a proper radial pressure can lead to a reduction in the cement lifespan. The radial cracking process generates local areas of high permeability around the outer face of the cement sheath. Our simulation results show at the shallower depths the cement matrices resist CO₂-bearing fluids more and this delays exponentially the travel time of CO₂-bearing fluids towards the Earth's surface. This is based on the evolution of CO₂ gas from the aqueous phase due to the reduction in the fluid pressure at shallower depths, and consumption of CO₂ in the reactions which occur at the deeper locations.

The aim of this paper is to compare the performance of three horizontal infill wells in a mature field, of which one is completed with autonomous inflow control devices (AICDs). The analytic results are based on the comparison of oil production rates; water cut development and water-oil ratio plots of the wells. All the wells in this study are producing from the same homogeneous sandstone reservoir.

Two of the horizontal infill wells are targeting attic oil in an area with low risk of gas production of which one of these wells is completed with slotted liners and the other with AICDs. Both are artificially lifted with high rate electrical submersible pumps (ESPs). The third horizontal well was placed in an area with higher gas saturation, where a completion with casing, cementation and perforation was used. The performance of the horizontal wells is compared against each other.

The use of active geo-steering successfully supported the well placement into the "sweet spot" of the reservoir due to real-time well path adjustments.

It was found that the AICDs choke back a high amount of fluid and keep the water cut at a stable plateau level. This observation underlines the key benefit of using AICDs as when comparing to the other producing wells without AICDs, the water cut is steadily increasing.

Therefore the use of AICDs is a real option for horizontal well completion.

This paper will be useful to those who are in a phase of early well planning, e.g. in a field (re-)development project and have to select the best well concept (e.g. slotted liner vs. AICDs). AICDs have proven their value even in a super-mature oil field by improving production. Further advantages and challenges during operation are discussed in this paper.

Analytically-derived criteria are presented for the orientation of fracture initiation from horizontal wellbores drilled in porous-permeable (poroelastic) media. This involves drilling-induced tensile fractures (DITFs) from non-perforated wellbores and completion-induced hydraulic fractures (CIHFs) from perforated wellbores with cylindrical perforation geometry. The criteria are developed considering the tangential stresses on two points (extremes) around the base of the perforation; one for the initiation of longitudinal fractures and another for the initiation of transverse fractures, with respect to the wellbore. In-situ stress state, wellbore pressure, and the formation's mechanical and poroelastic properties are independent variables that are shown to control the orientation of the initiated hydraulic fractures; the dependent variable.

The DITF orientation can be used to constrain the magnitude of the maximum horizontal stress; the most difficult aspect of the in-situ stress tensor to constrain. Transverse CIHF initiation only occurs over a narrow wellbore pressure-at-breakdown window, while longitudinal initiation occurs at comparatively higher wellbore pressures. However, transverse CIHF initiation occurs more frequently than transverse DITFs, because the presence of perforations aids transverse fracture initiation. The region of the in-situ stress states where transverse initiation is promoted is shown in dimensionless plots for perforated and non-perforated wellbores. Fracture initiation criteria for specific cases presented can be used to predict the orientation of fracture initiation in oilfield operations.

The orientation of CIHFs controls the productivity of hydrocarbon reservoirs. Productivity from low permeability formations is greatly improved having multiple fractures oriented transversely rather than longitudinally, relative to a horizontal wellbore. Fracture initiation often follows a plane different to the final fracture propagation plane. Stress re-orientation in the near-wellbore region may promote fracture initiation of different orientation than the orientation dictated by the far-field stresses. The range of in-situ stress states in which transverse fracture initiation is promoted increases as Biot's poroelastic coefficient, α_B decreases and formation Poisson's ratio, ν increases. Case studies ran on unconventional shale plays and the likely orientation of fracture initiation from perforated horizontal wells is discussed. The results indicate higher confidence in transverse CIHF initiation when poroelastic rocks are considered, compared to previous models developed for linearly-elastic rocks, nevertheless numerical modeling is necessary to assess the criterion, because of approximations involved in its derivation.

The Bowland Basin in Northern England contains a thick shale gas section (>5,000 ft) estimated to hold over 1300 TCF of total original gas in place of shale gas resource. In 2017, Cuadrilla Resources drilled a S-shaped pilot well, Preston New Road-1 (PNR-1), located in Lancashire, NW England. The plan was to drill, core, and log the Bowland Shale sequence with the primary objective to select the optimum landing depth for a subsequent side-tracked horizontal section (PNR-1z) of up to 3,280 ft length to be completed for multi-stage hydraulic fracturing. Another multi-stage horizontal well, PNR2, was also planned to be drilled afterward targeting a different stratigraphic horizon. Three vertical wells (PH-1, GH-1 and BS-1) were previously drilled in the Bowland Basin to a depth of 8,860-10,500 ft. Delays were encountered in the drilling of these wells due to multiple borehole stability problems. Specifically, in GH-1, the well required a side-track to reach the target depth. With the plan to drill four horizontal wells at Preston New Road, the first horizontal wells ever to be drilling in the Bowland shale, a rigorous geomechanical study was required to provide valuable insights for optimisation of the drilling programme.

A pre-drill geomechanical model was developed for the PNR-1 pilot well using advanced interpretation of available data and the gained experiences from the offset wells. A comprehensive pore pressure interpretation showed that Bowland shale is significantly over-pressured (0.69 psi/ft). The model was backed up by the observed splintery cuttings and gas shows in offset wells. It was concluded that this abnormal pore pressure combined with a tectonic strike-slip stress regime (with large horizontal stress anisotropy) and intrinsic anisotropic shale properties were the primary causative factors for drilling incidents. As a result of this study, the PNR-1 was successfully drilled and completed with minimal borehole stability problems despite the presence of narrow operating mud weight window in several stratigraphic intervals. The data acquisition program conducted included 114m of core from Upper and Lower Bowland shales, with the required logs for updating the geomechanical model. A comprehensive rock mechanics testing program was designed and conducted which resulted in better characterizing the anisotropic elastic properties and strength parameters of the Bowland Shale. This information was used to update the geomechanical model and aid the optimum landing decision depth of 2,180m for PNR-1z. A successful XLOT prior to drilling the 6" lateral section provided valuable data for further calibration of the stress model. The updated model was then used to develop safe operating mud weight window for PNR-1z, which helped drilling of the horizontal section to the TD at 11,233 ft MD (7,457 ft TVD) with no notable drilling problems.

This paper presents a summary of the geomechanical work performed for successful drilling and hydraulic fracturing operations in the Preston New Road exploration site and the outcomes and achievements.

A high rate of penetration (ROP) is considered one of the most sought-after targets when drilling a well. While physics-based models determine the importance of drilling parameters, they fail to capture the extent or degree of influence of the interplay of the different dynamic drilling features. Parameters such as WOB, RPM, and flowrate, MSE, bit run distance, gamma ray for each rock formation in the Volve field in the North Sea were examined ensuring an adequate ROP while controlling the tool face orientation is quite challenging. Nevertheless, its helps follow the planned well trajectory and eliminates excessive doglegs that lead to wellbore deviations. Five different Machine Learning algorithms were preliminary implemented to optimize ROP and create a less tortuous borehole. The collected data was cleaned and preprocessed and used to structure and train Random Forest, Support Vector Regression, Ridge Regression, LASSO, and Gradient Boosting, XG boost among others and the appropriate hyperparameters were selected. A successful model was chosen based on maximized ROP, minimized deviation from planned trajectory, and lower CPF. An MAEP of 15% was achieved using GBM boost followed AdaBoost. The algorithms have demonstrated competence on the historical dataset, accordingly it will be further tested on blind data to serve as a real-time system for drilling optimization to enable a fully automated system.

Drilling wastes generated in large volumes is recognized to have many effects on the environment. Several techniques have been applied by the oil and gas industry to overcome the impacts of drilling waste on the environment, an example of these techniques is using environmental friendly drilling fluid additives.

This work investigates the potential of using White Sunflower Seeds’ Shell Powder (WSSSP) as an environmental friendly drilling fluid additive. This material was prepared in-house. Experimental evaluation has been carried out to investigate the ability of WSSSP to enhance several properties of water-based drilling fluid under two different pH conditions. The WSSSP was first evaluated at 9.3 pH then the pH was increased using sodium hydroxide to 11.5. Several properties of drilling fluid were measured. The measurements included testing the rheological properties using viscometer, measuring the filtration using standard low-pressure low-temperature filter press, the pH using pH tester, and other important properties.

The findings of this work showed that WSSSP in 9.3 pH environment reduced the fluid loss by 18% and 30% when 1% and 2% concentrations of WSSSP were added, respectively. This reduction in fluid loss was along with forming a thin filter cake. The filter cake thickness of the reference fluid was decreased from 3 mm to 2.14 mm and 1.9 mm at 1% and 2% concentrations of WSSSP. Additionally, WSSSP resulted in increasing the plastic viscosity (PV) compared to the reference fluid by 33.33% at 1% and 2% concentrations. While the yield point (YP) was increased by 22.22% and 44.44% when 1% and 2% concentrations of WSSSP were added, respectively. Both the initial and final gel strengths were increased by 27.27%, 44.44 %, 7.14% and 14.28% at 1% and 2% concentrations, respectively. Moreover, the results in 11.5 pH emphasized the efficient performance of WSSSP, and it showed better improvement in the filtration specifications and the rheological properties. In other words, PV, YP, and gel strength were significantly increased; while the fluid loss was very low and the filter cake was very thin at 11.5 pH condition compared to 9.3 pH condition for the same concentrations, proving the ability of WSSSP to perform better under higher pH condition.

The significant enhancement in the rheological and filtration properties, suggesting the applicability of using this additive as a rheology modifier and filtration control agent. These results showed the potential use of WSSSP as an alternative for some of the toxic materials used today in the oil and gas industry. This work demonstrates that this additive will help to reduce both the impact on the environment along with reducing the cost of drilling fluid and drilling waste handling.

Japan Agency for Marine-Earth Science and Technology (JAMSTEC) operates the scientific deep-sea drilling vessel Chikyu for scientific studies on past climate changes, long-term crust transportation, biological and abiotic processes associated with hydrocarbon production, and earthquakes, the last being one of the most important research topics. Chikyu conducted the Japan Trench Fast Drilling Program (JFAST) to obtain core samples from sediment layers under the seabed for study on the large Tohoku earthquake which triggered the devastating tsunami in 2011. Chikyu has also started to conduct the Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) as the Nankai Trough is one of the most active earthquake zones. As one of the primary goals of scientific drilling is to evaluate sediment properties, it is highly beneficial to characterize the lithology of the drilling layer during drilling operations. Even an approximation of these properties could potentially provide valuable information for conducting coring operations. Thus, a previous study attempted to discuss the properties of sediment layers using surface drilling data, and estimated the shear stress of the sediment. In this study, we summarize the method applied in the previous paper for estimating the torque at the drill bit from the surface measured drilling data for NanTroSEIZE deep riser drilling operation. This data was then used to directly calculate the shear stress of the sediment. The drilling torque at the bit differed from the surface torque, where this difference increased with increasing drilling depth. Our estimations of the drilling torque were validated using torque data obtained from logging while drilling (LWD) operations. We also used machine-learning approaches to predict the lithology, where learning data was created from surface drilling data and lithology information from core samples obtained during past scientific drilling operations. Machine learning was then applied using neural network algorithms by tuning the number of layers to create a predictive model. This paper discusses the preliminary attempt to predict the lithology using machine-learning approaches for NanTroSEIZE and JFAST data.

As drilling automation has transformed from a blue sky vision to a reality, so has the industry's understanding of the depth and breadth of automation needs and opportunities. The focus is no longer solely on-bottom drilling performance but now considers the entire lifecycle of well construction. This workshop will examine the following key areas in terms of pragmatic solutions that are either available today or are coming in the near future. Individual case studies within each session will be presented that provide a foundation for what is available today, and what will be available in the near term. This workshop will bring together operators, drilling data solution experts, as well as service company and drilling contractor personnel to identify and discuss challenges to accelerating adoption of these solutions in the industry.

Global deepwater exploration and development activity is on the upswing driven by an anticipated long-term increase in worldwide demand for hydrocarbons. Recent technological innovations have helped the industry to improve the economics and reliability of deepwater projects. Business and technical drivers vary by locations, but all rely on the continuing cost-effectiveness of efficiently designing, drilling and completing wells. Techniques are being adopted that involve advanced interdisciplinary planning and real-time adjustments to deliver highly productive wells. This workshop will have interactive sessions on new technologies, current practices, regional issues and critical challenges related to both drilling and completions in deepwater.

This paper describes an approach for optimizing the number and type of drilling centers required to enable the development plan to be flexible in design to accommodate infrastructure, facilities, drilling, and subsurface constraints. This paper investigates how decisions made through reservoir evaluation and drilling-and-completion planning affect the design of subsea production systems and, in turn, the design of production hosts.