Al-Nakhli, Ayman (Saudi Aramco) | Tariq, Zeeshan (King Fahd University of Petroleum and Minerals) | Mahmoud, Mohamed (King Fahd University of Petroleum and Minerals) | Abdulraheem, Abdulazeez (King Fahd University of Petroleum and Minerals) | Al-Shehri, Dhafer (King Fahd University of Petroleum and Minerals) | Murtaza, Mobeen (King Fahd University of Petroleum and Minerals)
Recent rise in global warming and fluctuations in world economy needs the best engineering designs to extract hydrocarbons from unconventional resources. Unconventional resources mostly found in over-pressured and deep formations, where the host rock has very high strength and integrity. Fracturing techniques becomes very challenging when implemented in these types of rocks, and in many cases approached to the maximum operational limits without generating any fracture. This leaves a small operational window to initiate and place the hydraulic fractures. Current stimulation methods to fracture these formations involve with adverse environmental effects and high costs due to the entailment of water mixed with huge volumes of chemicals such as biocides, scale inhibitors, polymers, friction reducers, rheology modifiers, corrosion inhibitors, and many more.
In this study, a novel environmentally friendly approach to reduce the breakdown pressure of the unconventional rock is presented. The new approach makes it possible to fracture the high strength rocks more economically and in more environmentally friendly way. The new method incorporates the injection of chemical free fracturing fluid in a series of cycles with a progressive increase of pressure in every cycle. This will allow stress relaxation at the fracture tip and correspondingly enough time for fracturing fluid to infiltrate deep inside the rock sample and weaken the rock matrix. As a result of which the tensile strength-ultimately the breakdown pressure of the rock gets reduced. The present study is carried out on different cement blocks.
The post treatment experimental analysis confirmed the success of cyclic fracturing treatment. The results of this study showed that the newly formulated method of cyclic injection can reduce the breakdown pressure by up to 24% of the original value. This reduction in breakdown pressure helped to overcome the operational limits in the field and makes the fracturing operation greener.
Deshpande, Kedar (Weatherford) | Celigueta, Miguel Angel (International Centre for Numerical Methods in Engineering) | LaTorre, Salvador (International Centre for Numerical Methods in Engineering) | Onate, Eugenio (International Centre for Numerical Methods in Engineering) | Naphade, Pravin (Weatherford)
Cuttings transport and hole-cleaning is a challenging issue associated with the efficiency of wellbore hydraulics and drilling operation. Traditional methods used to understand hole cleaning problems are based on field observations and extensive flow loop testing to formulate empirical correlations and mechanistic models. The focus of this study is to create digital twin utilizing advanced simulation techniques that provides better insight for cuttings transport and hole-cleaning. This study explores the use of Eulerian-Lagrangian based numerical techniques to estimate critical flow rate needed for efficient hole cleaning. Digital twin for the cuttings transport is formulated utilizing three dimensional Navier stokes equations employing combination of Eulerian and lagrangian approaches to model the drilling mud flow and cuttings interaction with the drilling mud, wellbore walls and between cuttings themselves. One of the important model to estimate the drag force on cuttings is modified for non-spherical cuttings shape coupled with non-newtonian Herschel Bulkley behavior of the drilling mud in this work. The influence of important parameters, such as fluid rheology, rotation of drill-string, and inclination of wellbore on the hole-cleaning process is investigated. Digital solutions are compared against the published data for Newtonian and non-Newtonian drilling fluids under different wellbore configurations. The advanced computational simulation involving novel drag force correlation and unique combination of numerical methods allowed to create digital twin for cuttings transport process accurately. The numerical strategy utilizing modified drag law showed a very good match with experimental results for straight vertical wellbore, the cuttings transport velocity estimated by digital solutions was within 5% difference of experimental results. Further upon validation, numerical results are successfully computed for drill -string rotation effects which clearly showed physics of cuttings transported efficiently with added energy due to rotation. The phenomenon of cuttings bed sliding in inclined and horizontal wellbores is also correctly simulated with the proposed drag law and numerical methods. The proposed methodology works without any issues with high concentration of cuttings and provides detailed insight into cuttings flow path and effect of various operational parameters on hole cleaning. Advanced computational simulations and modification of drag force law assisted in formulating digital twin that provided excellent insights in understanding effects of operational parameters for efficient hole cleaning.
Al Hosani, Mariam Ahmed (ADNOC Onshore) | Masoud, Rashad Mohamed (ADNOC Onshore) | Al Beshr, Huda Abdullatif (ADNOC Onshore) | Latif, Mohd Anwar (ADNOC Onshore) | Al Hammadi, Shamma Jasem (ADNOC Onshore) | Khalil, Ihab Nabil (ADNOC Onshore) | Al Bairaq, Ahmed Mohamed (ADNOC Onshore) | Al-Ameri, Ammar Faqqas (ADNOC Onshore) | Nasreldin, Gaisoni (Schlumberger) | Ni, Qinglai (Schlumberger) | Rodriguez-Herrera, Adrian (Schlumberger) | El Mubasher, Husham Kamal El Din (Schlumberger) | Corona, Mauricio (Schlumberger) | Sinha, Ravi Kumar (Schlumberger) | Subbiah, Surej Kumar (Schlumberger) | Hussein, Assef Mohamad (Schlumberger) | Karamalla, Babikir Mubarak (Schlumberger)
The growing appreciation of the effects of production-induced stress changes on reservoir performance has concentrated the minds of many people on the potential value of using geomechanical modelling to predict and quantify these effects for making life-of-reservoir decisions—relating to compaction mitigation and completing new wells.
This paper is concerned with well integrity analyses for compacting reservoirs—focusing specifically on a new area of predictive geomechanical modelling realised using the finite element method. The innovative workflow presented offers significant improvements and, for the first time, captures some of the realities of the construction process. It takes into consideration both the formation and completions by integrating 3D near-wellbore geomechanical modelling with cementing simulations and casing integrity analyses. Specifically, casing eccentricity and cement contamination data are taken from numerical cementing simulations carried out to re-create the conditions in wells with different trajectories. Moreover, formation mechanical properties, pore pressure and stress states from the time of drilling till the end of a simulated production schedule are taken from a calibrated field-scale geomechanical model and subsequently used to create high-resolution 3D near-wellbore geomechanical models.
The case study presented in this paper concerns a giant onshore field with multiple stacked reservoirs—containing a variety of hydrocarbons and experiencing different levels of depletion. The main interest is in conducting comprehensive casing and cement integrity assessments—particularly for wells located in compacting reservoir zones. A persistent challenge for geomechanical modelling and prediction is the availability of calibration data. This paper reduces uncertainty by presenting results concerning sensitivity analyses for a variety of completion conditions—including different levels of casing eccentricity, different degrees of cement contamination and different extents of casing corrosion.
Barros, Adelson (Adnoc Offshore) | Alaleeli, Ahmed Rashed (Adnoc Offshore) | Hamidzada, Ahmedagha (Adnoc Offshore) | El Hassan, Azza (Adnoc Offshore) | Melo, Alexandre (Adnoc Offshore) | Orfali, Mohd Waheed (Schlumberger) | Phyoe, Thein Zaw (Schlumberger) | Salazar, Jose (Schlumberger) | Kapoor, Saurabh (Schlumberger) | Kondo, Kazuyoshi (Schlumberger)
Lost circulation (LC) is an expensive and time-consuming problem. It's desirable to minimize losses before cement job to ensure good cement coverage and maximize well integrity. But quite commonly, wells experience induced losses just before cementing, during casing running and circulation. In such a scenario, the options to control losses have been few, with limited results. The paper demonstrates a viable solution that can be successfully applied to reduce or eliminate such induced losses during the cement job.
To effectively solve lost circulation with the correct technique, it is necessary to know the severity of the losses and the type of lost circulation zone. In UAE fields, the loss rates range from 150 bbl/h to more than 700 bbl/h in the 17½- and 12¼-in open hole sections. During cementing operations, lost circulation causes reduced top of cement, poor zonal isolation, and risks to drill ahead. To solve this problem, a composite fiber-based spacer system based on a novel four-step methodology was designed using advanced software. Before a field trial, rigorous lab-scale and yard-scale testing was conducted to optimize the application.
Initially, no losses were witnessed while drilling the 12¼-in section. But during casing running and circulation, severe losses of 150 bbl/hr were induced. To counter these losses, the specially designed fiber-based lost circulation spacer system was pumped ahead of the cement slurry using standard surface equipment. At the beginning of the displacement—while cement and spacer were still in the casing string—the loss rate increased to 700 bbl/hr (total losses). This high loss rate in the crucial intermediate section would normally have resulted in costly remedial operations, loss of mud and cement, and expensive rig time. It was observed that the loss rate remained at 700 bbl/hr until the lost circulation spacer arrived at the loss zone. Subsequently, the loss rate kept on declining finally resulting in full returns during remaining displacement. The designed excess of cement was received as returns, thereby ensuring the desired top of cement at surface. This proved that the fiber-based spacer was effective in curing the losses. An advanced cement bond log showed complete cement coverage over the entire section. This further proved the spacer's effectiveness in achieving all well integrity objectives.
The successful application of the engineered fiber-based lost circulation control spacer during primary cementing demonstrates a reliable solution to the challenge posed by losses induced immediately before a cement job. The system is easy to deliver and design and can plug the fracture network in the formation during the cement job. Globally, this engineered composite fiber-blend spacer has proved to improve performance during cementing operations by healing losses to maximize well integrity.
Cai, Zhenzhong (Tarim Oilfield Company, PetroChina) | Zhang, Hui (Tarim Oilfield Company, PetroChina) | Yuan, Fang (Tarim Oilfield Company, PetroChina) | Yin, Guoqing (Tarim Oilfield Company, PetroChina) | Wang, Haiying (Tarim Oilfield Company, PetroChina)
The Kuqa depression located in northern Tarim Basin is the second largest natural-gas field in China, however, drilling engineering is faced with extremely complex geological conditions, such as complex structural movement history, complex formation conditions (huge thick gypsum salt rock, and different thickness of alternating sand/shale sequences and conglomerate), abnormal high pore pressure systems and strong anisotropy in situ stress. These complex geologic conditions result in severe wellbore instability problems.
An integrated research was conducted combining geology, geomechanics and drilling engineering to solve drilling problems caused by complex geological conditions. Firstly, geomechanical models are established according to the geological characteristics of different formations to get orientation and magnitude of stress, pore pressure and rock mechanical parameters. Secondly, based on rock mechanics experiments and wellbore information, the geomechanical mechanism research of wellbore instability was carried out under complex geologic conditions. Finally, the geomechanical model, wellbore stability parameters and the mechanism of drilling problems are applied to the drilling engineering design optimizing mud parameters, wellbore structures and trajectory of high deviation wellbore.
It is shown that geomechanical approach can improve wellbore stability and drilling rate. (1) For the uppermost conglomerate formation, according to the experimental study of the failure mechanism of conglomerate, accurate mud density is the key avoiding causing extension fracture around conglomerate grains. (2) The mechanical stability of borehole in alternating sand/shale sequences is good, but it is easily affected by hydration. Therefore, high quality mud properties can be matched with low mud density to maintain wellbore stability and improve drilling rate. (3)The interior of gypsum-salt sequences is divided into six lithologic sections. Based on the detailed analysis of different lithology, an in-situ stress model is established optimizing the mud density to find a balance between creep resistance and preventing from lost circulation. (4)Pay zone belongs to fractured sandstone under strong stress background. It shows strong anisotropy in stress field and rock strength. The mud density window determined by this mechanism can not only maintain wellbore stability and prevent lost circulation, but also protect reservoir.(5)The feasibility of highly deviated well was demonstrated based on geomechanical approach. And the wellbore trajectory was optimized in four aspects: avoiding shallow fracture, maintaining wellbore stability, traversing more effective fractures, and easy fracturing after drilling.
Geomechanical research under complex geologic conditions promoted the recognition of the mechanism of wellbore instability, and optimized the program of drilling engineering. The drilling incidents of formation above salt were reduced by 50% and the non-productive time was reduced by more than 20%. At the same time, this research project also promotes the successful implementation of the first highly deviated wells which provided a new way to further improve the gas productivity in this area.
Al-Nakhli, Ayman (Saudi Aramco) | Tariq, Zeeshan (King Fahd University of Petroleum and Minerals) | Mahmoud, Mohamed (King Fahd University of Petroleum and Minerals) | Abdulraheem, Abdulazeez (King Fahd University of Petroleum and Minerals) | Al-Shehri, Dhafer (King Fahd University of Petroleum and Minerals)
Current global energy needs require best engineering methods to extract hydrocarbon from unconventional resources. Unconventional resources mostly found in highly stressed and deep formations, where the rock strength and integrity both are very high. The pressure at which rock fractures or simply breakdown pressure is directly correlated with the rock tensile strength and the stresses acting on them from surrounding formation. When fracturing these rocks, the hydraulic fracturing operation becomes much challenging and difficult, and in some scenarios reached to the maximum pumping capacity limits. This reduces the operational gap to create hydraulic fractures.
In the present research, a novel thermochemical fracturing approach is proposed to reduce the breakdown pressure of the high-strength rocks. The new approach not only reduces the breakdown pressure but also reduces the breakdown time and makes it possible to fracture the high strength rocks with more conductive fractures. Thermochemical fluids used can create microfractures, improves permeability, porosity, and reduces the elastic strength of the tight rocks. By creating microfractures and improving the injectivity, the required breakdown pressure can be reduced, and fractures width can be enhanced. The fracturing experiments presented in this study were conducted on different cement specimen with different cement and sand ratio mixes, corresponds to the different minerology of the rock. Similar experiments were also conducted on different rocks such as Scioto sandstone, Eagle Ford shale, and calcareous shale. Moreover, the sensitivity of the bore hole diameter in cement block samples is also presented to see the effect of thermochemical on breakdown pressure reduction.
The experiments showed the presence of micro-fractures originated from the pressure pulses raised in the thermochemical fracturing. The proposed thermochemical fracturing method resulted in the reduction of breakdown pressure to 38.5 % in small hole diameter blocks and 60.5 % in large hole diameter blocks. Other minerology rocks also shown the significant reduction in breakdown pressure due to thermochemical treatments.
El Hassan, Azza (ADNOC Offshore) | Alaleeli, Ahmed Rashed (ADNOC Offshore) | Hamidzada, Ahmedagha (ADNOC Offshore) | Jose De Barros, Adelson (ADNOC Offshore) | Al Katheeri, Yousif (ADNOC Offshore) | Bin Tarsh, Fatima (BHGE) | Aliyeva, Gunay (BHGE)
It is common to be faced with severe losses prior to cementing the 9 5-8 in. intermediate casing in an offshore field in UAE. Intermediate casing covers weak zones and as a results there is always a high risk of formation breakdown and induced losses while running the casing and before it reaches intended setting point. The average losses experienced during drilling the 12 1-4 in. hole may exceed 100 BPH.
The main challenge in the case reviewed in this paper was that the formation was fracturing during casing running, compromising ability to achieve proper zonal isolation and successful cement job execution.
To address the challenge a special LCM Spacer system was proposed, designed to minimize or eliminate the losses during the primary cement job by offering superior sealing capabilities. This LCM Spacer system can easily mitigate loss circulation while cementing, based on ultra-low invasion technology forming a barrier across loss zones. It creates a film across formation walls and reduces the loss circulation ranging from partial to total losses on permeable, fragile, weak formation, natural fractures and depleted reservoirs. It also improves wellbore stability and ECD’s along the wellbore and expected loss zones.
The LCM Spacer system was designed and implemented based on the well conditions, design guidelines and previously recorded global success of the system applied in similar applications.
Garzon, Jorge (ExxonMobil Upstream Research Company) | Hsu, Sheng-Yuan (ExxonMobil Upstream Research Company) | Shenoy, Karthik (ExxonMobil Bengaluru Technology Center) | Tenny, Matthew J. (ExxonMobil Upstream Research Company) | Meier, Holger A. (ExxonMobil Upstream Research Company)
Wells that are used to recover hydrocarbons from reservoirs are subjected to large amounts of complex geomechanical loads that may compromise the well's integrity over its operating lifetime. While the reservoir depletes, the pore pressure in the rock reduces and the effective stress in the rock formation increases. As a result, the rock deforms and the reservoir experiences an overall volume reduction (compaction). Under such compaction, any well casing experiences a substantial amount of compressive and shear stress/strain in all directions. In order to ensure safe operation of a well, it is necessary to impose operational limits (drawdown and depletion) so that stresses imparted on the casing do not exceed the casing strength. This problem has been studied in the past [
This technology has been applied to a number of business units within ExxonMobil, allowing us to establish practical drawdown/depletion limits. In this paper, we discuss a field example of this approach.
Moiseenkov, Alexey (Petroleum Development Oman) | Smirnov, Dmitrii (Petroleum Development Oman) | Mahajan, Sandeep (Petroleum Development Oman) | Al Hadhrami, Abdullah (Petroleum Development Oman) | Al Azizi, Issa (Petroleum Development Oman) | Shabibi, Hilal (Petroleum Development Oman) | Balushi, Yousuf (Petroleum Development Oman) | Omairi, Mahmood (Petroleum Development Oman) | Rashdi, Mansoor (Petroleum Development Oman)
There have been many oil and gas field discoveries in the Cambrian Ara Group intra-salt carbonate rocks in the South Oman Salt Basin. These carbonates represent self-charging petroleum system with over-pressured hydrocarbon accumulation in dolomitized rock encased in the salt. Drilling and completion wells going through salt is challenging. Salt creeping behavior results in issues of stuck pipe during drilling operations, casings deformation and collapse that have led to well suspension and abandonment.
The full set of the available historical data analyzed to identify magnitude and history of the problem. The study conducted to estimate of salt creep magnitude, to assess the effect of the salt creep on cement quality, drilling and completion risks. The risk of salt creep on the drilling, completion and long-term well integrity was evaluated with multi-disciplinary integration of geological, geomechanical, petrophysical and well engineering aspects to minimize and mitigate the salt creeping risks. In addition to identify root cause for completion failure and providing recommendations to drilling practices, cementation and completion design that can improve well delivery process.
Salt creep behavior presents drilling challenges associated with excessive torque, stuck pipe, casing deformation, and poor cementing job. Salt creep associated risks to drilling and well integrity should be managed and mitigated. Key study findings captured for wells designs were: Salt creep rate increases with depth, salt thickness and differential stress (function of MW) Non uniform loading decreases the collapse rating of the casing and results in casing deformation Non-uniform loading likely due to poor cementing, interface between rigid carbonate intervals and salt, and irregular open hole quality.
Salt creep rate increases with depth, salt thickness and differential stress (function of MW)
Non uniform loading decreases the collapse rating of the casing and results in casing deformation
Non-uniform loading likely due to poor cementing, interface between rigid carbonate intervals and salt, and irregular open hole quality.
Studied casing collapse cases could likely be attributed to several factors or combinations of factors such as salt mobility behavior, drilling with low MW, poor cement jobs and loss of internal hydrostatic support for the casing after cement job between liners lap. The improved multi-disciplinary understanding of salt creep is vital to reduce drilling and completion costs, unnecessary well abandonment and achieve good life cycle well integrity i.e. avoid extra side-track and workover cost due to integrity issues. The best practices and conclusions summarized in the study for drilling and completion design expected to benefit the exploration and development projects for the salt encased carbonate reservoirs around the globe.
Bermudez, Romulo (ADNOC Offshore) | Abdelkerim Doutoum, Mahamat Habib (ADNOC Offshore) | Al Azizi, B. (ADNOC Offshore) | Nour, Mahmoud (Halliburton) | Medina, Ruben (Halliburton) | Bereikaa, Hesham (Halliburton) | Rocha, M. C. (Halliburton) | Nasrallah, M. M. (Halliburton)
While drilling through the initial section of extended reach drill (ERD) wells in Abu Dhabi where the trajectory requires a high inclination across a recognized loss zone various options were required to be assessed to maximize efficiency while balancing risks. Factors such as loss rate, capability of mixing fluid, necessary density to help prevent flow from a shallow water-bearing zone, and rig time, where all necessary and key factors to consider in the design process.
For this UAE field with common losses in the surface casing, brine capping was determined the best solution to continue drilling without generating nonproductive time or creating a possible wellbore instability issue when unable to keep up with building mud to offset mud losses. For wells with a higher inclination angle, when the loss rate reached the point where it was not possible to prepare the fluid to keep up with losses, it was necessary to identify a different solution to cure or significantly reduce the losses and enable the hole section to be drilled without potential operational risks.
For vugular/fractured porosity formations, using tailored particle size materials was unsuccessful for curing the losses. Therefore, a unique solution was implemented by combining two different systems to battle the losses: a swelling polymer lost-circulation material (LCM) that hydrates and helps reduce flow velocity into the formation, followed by a shear-rate rheology-dependent cement system that is a tunable and tailored slurry with thixotropic properties, which stops losses and develops low compressive strength. With this combined solution, the drilling process was successfully resumed and completed.
The usual loss rate for this particular vugular argillaceous limestone formation is between 600 and 800 bbl/hr while drilling. Once the solution was successfully implemented, losses were reduced to 15 bbl/hr. The technique was performed on a second well, applying the lessons learned from the first attempt, and the unique solution achieved a dramatic reduction of losses to 2 to 6 bbl/hr. The cost and effectiveness of the treatment demonstrated that this solution is best for optimizing the drilling process for this particular condition.
Applying a swelling polymer LCM and the shear-rate rheology-dependent cement system cured losses for an argillaceous limestone formation with fractured/vugular porosity. It is the first global application of this combined solution.