Loss of barrier assurance and primary containment occurrences whether downhole or at surface have impacted safe well operation and production funnel significantly. Complex well head design, inadequate cement behind casing, threat of shallow gas presence and multiple downhole tubulars leaks are some of the common perils in sustaining the production. Apart from frequent pressure monitoring, risk assessment and mitigation plans to tackle the issues head-on, a new fresh perspective is required to manage well integrity and diagnostic holistically. This paper will highlight application of geochemical method as the new eye to trace source of well integrity issues and emulates forensic engineering to investigate well barrier failures. Crude and gas compositional analysis from C1 up till C36 carbon chain plays a key role in determining the possible scenarios of leak paths and type of fluid expelled from the wellbore. The best forensic analysis could be produced utilizing multiple samples which represent different stages of well life starting from open-hole exploration drilling, development, production and towards the well abandonment stage. Comparing samples composition at each stage with reference to the baseline while evaluating the existing or newly acquired cement bond and diagnostic logs will help to complete the lingering puzzle. Results showed that the origin of the fluid samples expelled from the wellbore are successfully traced in a much more economical way with faster turn-around time compared to the conventional diagnostic method. It helps to point out the most likely well integrity elemental failure which has triggered immediate actions to revive the production. Plan to feed in the cash flow has been accelerated 6 months ahead through work-over activities and number of unhealthy well strings has been reduced by 12%. Production deferment is also reduced by half million ringgit equivalent value. In a nutshell, the case studies provide an eye-opening insight towards predictive and quantitative well integrity solutions to support production. Forward looking the geochemical forensic method can be further tailored for strategic well diagnostic solutions as more data comes in. Time to action could be further reduced with the introduction of advanced on-site analysis technology to boost the restoration efforts.

In stimulated carbonate formations, one damage mechanism is the loss of near wellbore rock compressive strength upon matrix acidizing. Improper designed acidizing jobs may excessively soften the rock and negatively impact the mechanical response of near wellbore rock during production. In this work, an integrated geomechanical workflow is presented and applied to optimize acid placement and fluid diversion treatment in a Middle East carbonate reservoir. The model consists of petrophysical characterization of the formation, coupled wellbore flow model, rock dissolution model, rock physical model, wellbore stress analysis and lastly production prediction. The model first simulates stimulation fluid movement within wellbore and couples it with transient flow in reservoir. The primary analysis determines the distribution of reactive fluid along the well and predicts porosity evolution across the reservoir domain upon stimulation. Then, the developed geomechanical engine simulates the mechanical behavior (compressional or shear failure) of stimulated rock under different stress conditions during production stage. This paper introduces an integrated geomechanical workflow to stimulate matrix acidizing and describe dynamic reservoir compaction and its influence on production performance, which varies significantly with the stress condition, formation types and design strategy. In the presented case study, various diversion techniques are analyzed, and overall production are compared to assess the stimulation efficiency by considering the effect of rock failure. The comparative analysis identifies an optimized diversion technique and design, which can minimize near wellbore rock failure and sustain production for a longer term. This model enables a reliable prediction of acidic fluid distribution and identification of key controlling parameters to maximize conductive reservoir volume and mitigate premature wormhole collapse. Depending on the diversion technique and reservoir conditions, the workflow can provide a proactive solution to improve matrix acidizing design to enhance overall recovery. The presented case study can aid to build a customized and optimized strategy for matrix acidizing for middle east carbonate formations.

A mechanical earth model was constructed for an oilfield in Kuwait that has a history of borehole related problems and prone to significant non-productive time in the highly deviated wells, the typical sidetrack wells took more than 100% of the time compared to the low deviated wells. The field is geologically complex, tectonically stressed with faults, fractures, unstable shales and anomalous pore pressures. Wells drilled within the structure are highly deviated with trajectories that almost parallel reservoir bedding planes, and that are aligned with the direction of minimum geomechanical stress. A comprehensive study was conducted to better understand the stability issues and to investigate the feasibility of drilling numerous additional high deviation wells. Data from selected offset wells was collated, analyzed and combined with field and regional information to construct a geological model which could then be used to predict and mitigate drilling related problems. The equivalent mud weight is arguably the most critical drilling variable and an element of the new plan would take account of stress dynamics and formation strengths to develop a mud program for vertical and horizontal sections. A geological model was developed using data from offset wells combined with field and regional knowledge. Well logs, mud logs and operational reports were analyzed, while unstable zones and failure mechanisms identified and incorporated into the earth model. A well plan was developed which included a comprehensive mud program and operational contingency actions for unplanned events. The planned well was drilled and monitored in real time, with emphasis on mud weight and mud rheology through the unstable and reactive shales. Multiple failure mechanisms such as stress induced wellbore instability, invasion of drilling fluids into weak bedding / micro-fractures and osmotic sensitivity, were found to be the root cause of wellbore instability across reactive shale formations especially during drilling of highly deviated wells. Correct mud weight and type prediction was one key factor during the drilling stage to keep the wellbore stable and deliver good borehole geometry, including the water phase salinity and fluid properties. The key objectives of the study were to define a safe MW program for the vertical and deviated sections of the planned well by conducting a wellbore stability study and to determine a real-time strategy to mitigate or manage wellbore instability problems as they arise. The paper describes the process of optimizing drilling practices and the application of real-time geomechanical monitoring for successful drilling. This application promises to open the prospect of drilling additional complex trajectory well while mitigating against non-productive time.

The ever more challenging environments in which new wells are to be drilled, the uncertainties of the current market, and the availability of effective secondary and tertiary enhanced recovery (EOR) technologies, make the extension of existing wells' life more advisable than drilling new wells. To properly and proactively manage the degradation of Well Barrier Elements (WBEs) over time, thus ensuring the extension of wells life, a specific methodology and software have been developed. The concept of "Wells Life Extension" not only requires to get an adequate knowledge of the current wells integrity status, but also to predict future critical WBE(s) in order to put in place ad-hoc preventive measures. The methodology described in this paper includes three main phases: Well Integrity Assessment, which evaluates today's well integrity status through a risk-based approach. Estimation of Wells Ageing, which estimates the residual well life based on the understanding of WBEs ageing mechanisms. Definition of Intervention Plan Options, in which wells are classified on the basis of specific parameters, and then prioritized for future interventions through a cost-benefit analysis. The implementation of such methodology has allowed Customers to find out the most appropriate actions to be carried out on their ageing wells, with the objective of keeping production performances and safely operating the wells in line with the planned targets. Moreover, it has enabled to properly plan such actions over time, on the basis of the risk levels associated to the failure modes of each WBE, thus preventing and mitigating the need of potentially expensive interventions and protracted downtimes. Furthermore, emergency situations that would even increase costs and/or failures impacts, have been prevented, mitigated, and proper monitoring and maintenance programs have been executed in order to manage risks over time. In summary, the overall benefit of the presented methodology and software consists in anticipating well integrity issues and extending wells life through a proactive and cost-effective approach, that can enhance assets reliability, improve safety levels and minimize both downtimes and costs associated to WBEs failures.

To reach many of the world's petroleum-rich formations, drilling must first penetrate challenging shale formations where wellbore instability frequently results in costly stuck pipe, lost circulation, non-productive time, and expensive sidetracks. One technology gaining traction through successful field usage is a wellbore stabilizing agent (WSA) to limit the invasion of drilling fluid and wellbore pressure into the formation. Using a WSA can assist in stabilizing shales, delivering trouble-free drilling, and reduce losses and non-productive time. The drilling team was assigned a challenging well involving the Mutriba Formation, a shale-limestone formation notorious for stuck pipe and lost circulation. Focusing on wellbore stability and minimizing of the destabilizing nature of invasive drilling fluid and wellbore pressure, the team utilized a wellbore stabilizing agent to stop fluid invasion at the borehole wall. This barrier, or "shield", minimizes formation damage and mitigates fracture growth which can lead to destabilization of the wellbore Constant monitoring and additions of the wellbore stabilizing agent resulted in a thin, tight, flexible HTHP filtercake and wellbore stability while drilling this challenging formation. The entire section through the Mutriba Formation was drilled with 100% returns and later casing was run without problems. No adverse wellbore conditions were encountered while tripping or drilling, and no non-productive time was lost in stuck pipe or lost circulation events. When compared to the offset well, the successful well using the wellbore stabilizing agent came in 7 days ahead of schedule and with a cost savings of more than 21% for the Mutriba section. Controlling wellbore instability, especially in shale and shale-composite formations, is a key element of successful drilling in many fields across the globe. Information on field-proven technologies, such as this wellbore stabilizing agent, are important to the continual improvement of drilling fluid to safely drill similar fields around the world.

Most drilling-related incidents are caused by unstable boreholes, whether they are caused by lost circulation, packoff, or stuck BHA and/or casing. One of the main objectives of this study was reduction in drilling incidents and associated Non Productive time (NPT) while drilling wells in a particular area of Kuwait, where often extremely challenging environments were faced due to wellbore instability arising from tectonic stresses, associated faults, fractures, complex structures, and anomalous pore pressure. Additional challenges were presented by a complicated and highly deviated well design, where planes of weakness of the formation being drilled and their relative angle with respect to the well path become crucial factors in assessing stability of the borehole. Multiple failure mechanisms such as stress induced wellbore instability, invasion of drilling fluids into weak bedding / micro-fractures and osmotic sensitivity, were found to be the root cause of wellbore instability across reactive shale formations especially during drilling of highly deviated wells. In lie of these challenges, a comprehensive study was conducted to overcome the wellbore stability issues and investigate feasibility of drilling Ahmadi wells of Kuwait at high deviation. Correct mud weight (MW) prediction was one key factor during the drilling stage to keep the wellbore stable and deliver good borehole geometry ( Figure 1 ). The key objectives of the study were to define a safe MW program for the vertical and deviated sections of the planned well by conducting a wellbore stability study and to determine a real-time strategy to mitigate and-or manage wellbore instabiity problems as they arise. The scope of work included root cause analysis of drilling events, development of mechanical earth models (MEM) for offset wells, integrating sections of the MEM from the offsets to the planned well trajectory, and a safe MW program for planned well. The paper describes the process of optimizing the drilling practices based on geomechanical outputs, to overcome serious drilling hazards and application of real time geomechanical monitoring for successful drilling. This application promises to open the prospect of drilling similar wells without complications and reduce NPT in Kuwait.

KOC planned to drill a challenging horizontal well in Ratqa field where there are serious limits to build deviation, reservoir navigation and hole instability. The candidate well was targeted into early Cretaceous Zubair reservoir, a highly laminated sand/shale sequence. Objective of this horizontal well is to target two highly depleted thin reservoirs (UCH and LCH) within Zubair, with a thick shale layer in between. While navigating the wellbore optimally through sweet spots within the reservoir units is a challenge, the risks of shale instability and differential sticking are other expected challenges during drilling. The target reservoirs sequence is around 8-10ft thick and there is 8ft thick interbedded shale separating the two sands. How to land the well properly inside the upper channel with optimum exposure of two sand units is one concern, and stability of interbedded shale at high angle is another concern. In order to mitigate these issues, pre drill geo-mechanical modelling was performed to predict the require mud weight and real time geo-mechanical monitoring was also carried out in conjunction with geo-steering. The resistivity contrast of these sands is around 70Ωm versus 10Ωm, which would give 9ft – 10 ft depth of detection (DOD) for azimuthal resistivity tool. This service would help to place the well optimally inside the reservoir and also provide early warning before exiting reservoir. The well was landed 7ft TVD inside the upper channel and continued building to 90° inclination in the lateral section with mud motor in order to build faster and also to prevent any stuck up with high configuration tool. The re-logged section confirmed that the wellbore already reached the base of upper channel. It was then decided to continue drilling to lower channel by crossing the interbedded shale using 9.5ppg mud weight in order to keep options open for running Inflow Control Devices (ICD). However, tight hole, over pull, pack-off, bit stalling, bigger size cavings etc. indicated poor wellbore condition. As drilling with lower mud weight already initiated shale instability it was then attempted to gradually increase the mud weight to avoid further deterioration of hole condition. It was then decided to sidetrack the section with a mud weight of around 12+ppg, as recommended by the pre-drill model. In addition, mud formulation was adjusted to block micro-fractures/invasion into shale to reduce differential sticking risk. Real-time wellbore stability monitoring was carried out including LWD log responses, cavings characterization, hole condition monitoring, etc. The wellbore was built to 89° inclination upon entering the lower channel as per correlation and was maintained inside the lower channel. The lateral section achieved 1,120ft long footage with a 78% exposure inside the sweet spot. Integrated real-time geo-steering and geo-mechanics successfully helped placing the well optimally in the target sands without hole instability.

This article attempts to summarize measures that are required to be adopted in order to have safe drilling practices mainly in unstable shale formation and have a smooth landing section in target reservoir below the shale. For the last three years in North Kuwait, the number of geo-steering jobs increased significantly and some encountered problems while drilling Wara shale that may end up in losing tools and eventually the hole itself. This paper focuses on information regarding problems encountered in geo-steering jobs and the best practices followed to achieve goals. Stratigraphically, Wara shale lies underlying Tuba and overlying Mauddud carbonates. It has thickness variation in between 80 to 110 feet TVD. Wara shale in North Kuwait is generally unstable and very sensitive to mud properties and creates instability of the wellbore. A wide range of drilling data from well placement jobs were documented and analyzed in order to get an idea of the behavior of shale section, how to drill safely across this layer and mitigate possible risks that may harm the well as well as the tool. Detailed scrutiny was done to compare the drilling parameters, log responses, inclination and trajectory direction between stable and unstable wells. The results were integrated with regional tectonic regime in the area. The methodology and learning curve continuously improved with assimilation of new drilling data and information. Integrated study on all aspects in drilling that involving geo-steering engineers, drilling team, geologists and field engineers on-site has enhanced the ability to understand the situation in the hole and ultimately able to provide faster decision. It was observed that there is strong relationship of building inclination, direction of the well and mud weight in some wells when crossing Wara shale. Wells that have East - West or Northwest - Southeast direction tend to be unstable when compared to wells in North - South or Northeast - Southwest direction. Low incident angle (high inclination) will mostly cause more problems in drilling than high incident angle due to longer section of exposure as well as overburden. Compressional tectonic regime of the area dictate the recommendation of well trajectory should go towards maximum horizontal stress. Recommended to cross it with low inclination and consequently approaching the target reservoir with high dogleg severity tool was to maintain the stability of the wellbore. These findings will help service provider and client to make proper planning, adopt best practice, take proper decision and thereby successfully execute well operations. Indeed saving rig and delivery time that fulfill business objectives as planned.

This project intends to develop an improved wellbore stability model based on poromechanics and non-equilibrium thermodynamics which describes the physico-chemical interactions between a multi-component drilling fluid and a reactive shale formation. Through finite element modelling, this model can be employed in wellbore stability studies in order to optimise drilling fluid formulation and mud weight selection. Specifically, we present the results of finite-element-finite colume based analysis of thermal and solute diffusion associated with wellbore heating and cooling effect on the reservoir system by drilling fluid over a period of time. Then, we solve the heat driven solute diffusion equation with thermal osmosis and solute diffusion coefficients. This preliminary investigation indicates a gradual but steady increase in temperature in the near wellbore region during during heat energy disspation from the far-field region. A reverse process was observed during the cooling process with both indicating a constant solute mass fraction over the time limit

This study systematically investigates the mechanical instability of a wellbore as a function of rock mechanical properties and in-situ earth stresses, and validates the predicted failures with post-drilling problematic wells. Results from this study will help to avoid wellbore instability related issues. Extended Reach Wells (ERD) were drilled in field X through shale formations inter-bedded by unconsolidated sandstone formations and carbonate formations which experienced severe wellbore instabilities. Rock mechanics lab tests were performed on preserved core samples and all the available well logs were obtained and subsequently analyzed thoroughly to develop the rock mechanics properties profile. Daily drilling reports were analyzed and this drilling history was used to evaluate the best failure criterion for modeling purposes. Accordingly, Mogi-coulomb was found to be the most appropriate failure criterion that matches the drilling history failures with predicted failures and can be used for more accurate future wellbore problem predictions. An industrial geomechanical software was used to build a Mechanical Earth Model (MEM). The software output was calibrated and validated with the observed failed wellbore condition in selected drilled wells. Subsequently, the root causes of different wellbore instability problems were identified. After preliminary validation of the MEM, the safe mud weight window for drilling future wells was predicted with respect to each formation by providing plots for different inclinations and azimuths. The safe mud weight windows for drilling in any inclination, azimuth and measured depth for Aruma, Rumaila, Ahmadi, Safaniya, Biyadh and Buwaib were found and reported. Furthermore, the safest mud weight window that works for the entire section at any inclination, azimuth and measured depth was discovered and reported for the fisrt time. Results from this study indicate that the predicted mud weight window profile could be adopted in future drilling operations for safe problem-free drilling in problematic formations.

Recent studies have shown that more than 50% of wells that are 15 years old or older have at least one casing string with sustained casing pressure. Cement sheath failure will result in sustained casing pressure, cross flow, lost production, collapsed casing, contaminated water zones and increased workover costs. Today, US federal regulation do not allow wells with sustained annular pressure to be plugged and abandoned. Remediation in these cases is both difficult and expensive. Therefore, utilizing a cement formulation which repairs itself in case of any failure under downhole conditions would be ideal for ensuring long-term well integrity and preventing the occurrence of sustained casing pressure. The objective of this paper is to review the self-sealing cement technology presented in the literature. This study manifests the latest novel laboratory equipment which allowed the cement to cure, get cracked and then seal under downhole conditions. The hydrophilic essence of this material provides a durable cement sheath to help ensure well integrity and zonal isolation for the life of the well. Mechanical properties testing could demonstrat the improved tensile to compressive strength ratio, lower Young's modules and higher Poisson's ratio. In addition, self sealing cement could self seal multiple times and therefore deliver a durable cement sheath in a wide variety of field cases.

The well design has been changed over last 55 years of development in Zubair Formation. It is the deepest producing Cretaceous reservoir in North Kuwait. This 1,400 ft thick formation was deposited in deltaic to Paralic depositional environments with complex sand/shale sequence, structural geometry, mineralogical composition and lateral extent. Drilling wells of any profile has been more difficult than the shallower reservoirs overlying it. The wells have witnessed high non-productive time due to severe wellbore instability issues in the form of stuck pipes, tight holes, hole pack-offs and jarring/fishing operations. During initial phase lasting over 4 decades, vertical wells were drilled to drain the oil column which was thicker in most part of the Field. With water encroachments from bottom and edge, thinner pay Sands in multiple but thin pays are needed to be exploited by maximizing reservoir contact with high angle multi-lateral wells for effective production. Drilling complications are inherent in Zubair since beginning even with vertical and deviated wells. Current transition to horizontal and high angle wells was possible with integrated studies. In the first phase of mitigating stability, responsible failure mechanisms for wellbore were identified: stress induced breakouts, washouts and cavings, failure and fluid invasion associated with shale bedding planes at high deviation and osmotic pressure transmission between Zubair shales and drilling fluid system. Water sensitivity of clays and presence of micro-fractures were also studied on cores of this trouble making formation. In the second phase, calibrated well based 1D Geomechanical models; 3D structural model with high definition faults, facies models indicating lithological changes and drilling experience of latest high angle wells were integrated into a 3D Geomechanical model. The model was tested with data from several offset wells and it was capable of explaining the wellbore failure of these wells. It was used predicting mud weight window for any proposed high angle well trajectories. Mitigation measures from the study included drilling with Oil Based Mud or High performance water based mud systems with model derived mud weights, micronized sealing polymer to seal-off the laminations and micro-fractures, marble grade Calcium carbonate or resilient graphite to plug wider fractures and high salinity of mud to avoid time-sensitive osmotic flow. The integrated study was implemented and six horizontal wells and a highly deviated well have been drilled successfully. The well designs and trajectories have been modified to drill along different azimuths of stress field with turns and up dip/down dip movements. Structurally complex and faulted blocks could be crossed effortlessly. The study has given further confidence to implement an aggressive field development plan for optimal depletion of undrained areas. Current strategy is to have vertical and deviated wells also for thicker reservoirs as they have the advantage of well interventions. The paper discusses complex reservoir architecture, drilling complications and how the integrated study helped to achieve a breakthrough in development planning.

The use of water-based drilling fluids to drill shale formations can cause wellbore stability problems as a result of the reaction of water with clay minerals. Examples of wellbore stability problems include shale disintegration, swelling and sloughing. Different types of clays give different types of problems. For example, when it is exposed to water, a shale sample with a high percentage of smectite tends to swell while another shale sample with a high percentage of kaolinite tends to disintegrate and disperse. Consequently, there will be higher solids loading in the wellbore. Hence, the chance to get the pipe stuck increases and the hole cleaning efficiency of drilling fluid decreases significantly. To combat the abovementioned challenges and study the shale rock to be drilled, a series of tests should be conducted. The selection of the testing procedures and fluids to test shale samples with has been selected mainly on empirical basis involving trial and error. Molecular modeling technique can be utilized before taking the shale samples to the laboratory to provide theoretical background on the rock-fluid interactions at molecular scale. One advantage of this approach is to gain better understanding of the rock-fluid interactions from theoretical point-of-view in order to explain why one shale inhibitor works and provides adequate inhibition for one shale sample but does not work properly for another sample. The second advantage is that having insights into the potential rock-fluid interactions can guide the research to include or exclude certain types of shale inhibitors and to shorten the trial and error procedure. These advantages provide a basis upon which future drilling fluids planning can be optimized to mitigate wellbore stability issues.

The United States National Science Foundation, engaging 29 researchers at nine institutions, has funded a Sustainability Research Network (SRN) focused on natural gas development. The mission of this Sustainability Research Network is to provide a logical, science-based framework for evaluating the environmental, economic, and social trade-offs between development of natural gas resources and protection of water and air resources and to convey the results of these evaluations to the public in a way that improves the development of policies and regulations governing natural gas and oil development. Currently, there are a wide range of estimates of the probability of shallow aquifer contamination. There are a series of independent events that must occur to allow hydrocarbon migration and estimates were made of these probabilities. An analysis of data from drilling in the Wattenberg field, CO was made to quantify the probability of contamination. It has been determined that there are five events that must each independently happen to allow the migration of fracturing fluids, and there are three events that must occur independently for the migration of hydrocarbons. The lower number of independent events, which must arise for hydrocarbon migration to occur, explains the infrequent, but well publicized natural gas migrations in poorly constructed wellbores, and the lack of such publicized events of hydraulic fracturing fluid contamination, which was confirmed by our analysis. The significance of these results is to help quantify the risks associated with natural gas development, as related to the contamination of surface aquifers. These results will help shape the discussion of the risks of natural gas development and will assist in identifying areas of improved well construction and hydraulic fracturing practices to minimize risk.

3D images of a wellbore generated in real time support drilling engineers to monitor wellbore profiles. Including the time as 4th dimension, 4D images can be used to analyze the evolution of the wellbore geometry as well as to support the drilling engineer in actuating appropriate counteractions in real time. Costly failures can be avoided more precise, alterations in the drilling practices to optimize the shape of the borehole will improve the drilling efficiency, or the driller is supported in making proper decisions such as reaming a critical zone or modifying the string rotation speed to reduce vibrations. This paper reviews tests and experiments, which have been performed using high frequency ultrasonic caliper sensors in different drilling fluids and wellbore conditions. Test results show that with the new design of an ultrasonic caliper tool velocity of sound can be determined in real time at the pressure and temperature of downhole condition. This will increase the accuracy of the measured diameter and the shape of the borehole in real time. In addition, a method for fast data transmission from down-hole to surface is presented and the best method for transmitting data to create the 4D images is discussed. Even with such technology improvements the ultrasonic caliper cannot provide absolutely accurate information for all drilling environments and conditions. Several operational factors, such as mud density, borehole wall roughness, and tool position in the borehole need to be considered in order to optimize the accuracy of the borehole caliper data. For this reason, robust circle fitting algorithms based on the Kasa method have been implemented. In combination with the new design of the caliper tool, the accuracy of the results has been strongly increased.