As the demand for natural gas continuously increases to meet electricity production needs, more alternative natural gas sources are usually required to cope with the increased demand in the summer months. In South Iraq, this situation is the main driver for exploiting economically feasible and efficient solutions in finding additional natural gas resources. As a result, the Iraqi government embraces the challenge by drilling deeper formations which are gas bearing, with limited experience in such fields. In the most recent appraisal campaign for these gas fields, performed in 2015 and 2016, one of the main challenges were bits and bottom hole assembly (BHA) failures while drilling through different interbedded and abrasive formations. Changing the bits type, BHA centralization, drive system and drilling parameters did not result in significant benefits. For the 17 ½" section, up to six (6) independent runs were required to successfully drill the entire section. The success was limited due to severe shocks and vibrations, high axial forces and high torque that caused failures on downhole mud motors and bits, leading to fishing operation and severe non-productive time. Other problems like unstable drilling parameters, extremely low rate of penetration (ROP) and poor wellbore quality were observed, leading to excessive reaming and backreaming as well as stuck pipe events and difficulties to maintain well verticality. To avoid and minimize the impact of these challenges, a comprehensive engineering team performed various finite element analysis on the interaction between BHA, drilling bit and formations drilled. The conditions on which the wellbore was maintained in the offset wells with its drilling fluids strategy and drilling parameters were reanalyzed. The bits selections were revised, identifying areas of opportunity to introduce fit for purpose technologies on cutters and bits profile. The ultimate challenge was to drill the full 1800 m of the section in one run avoiding any BHA related failure. The results exceeded expectations in the fourth well, where no BHA related failures were observed, and the drilling bit was able to drill the full 1800 m. Connection practices were also optimized. This enabled an improvement in the wellbore quality based on caliper logs. Improved wellbore conditions allowed a smooth casing run and consecutive cement job. This paper will discuss the engineering methodology followed to achieve this important milestone in one of the few gas fields in Iraq. It will go through the details of the technologies implemented on BHA analysis, bit selection, drilling parameters optimization and drilling fluids strategy implemented. The objective of this paper is to share with the oil and gas industry a methodical approach for efficient drilling, and how to address drilling challenges with technology introduction and engineering design.

Drilling and cementing through surface sections with highly active shallow gas formations is seriously challenging. In order to save employees lives and maintain a safe working environment, wells are designed with careful consideration of mud weight, drilling and mud parameters, while utilizing advanced monitoring techniques during well execution. While drilling, if well flow situation occurs, killing the well using industry accepted killing methods is not always possible as proper blowout prevention systems are not yet installed at the wellhead. For such wells, a diverter system must be utilized, enabling closing the well and diverting the flow to a safe distance away via two large sized vent lines for the rig crew to evacuate the work area safely. In cases where shallow gas contains flammable hydrocarbons, evacuation is mandatory. In some places in the Middle East however, the shallow gas has different properties, being inert nonflammable Nitrogen (N2) gas, eliminating both explosion and fire risks. Nevertheless, handling high pressure blowouts introduce severe risks to crew members, equipment, and the environment. In case drilling is decided to be initiated in the high-risk shallow gas area, all precautions must be taken to prevent gas flow whilst drilling. This is possible by adequate mud weight selection allowing sufficient overbalance throughout the complete drilling, casing, and cementing operations ensuring shallow gas zone is properly sealed and isolated before drilling deeper intervals. In a large Middle East field, a large number of wells have been drilled with some areas having shallow nitrogen (N2) gas at high pressure in formations lying at 200-800 ft depth. In such areas, having shallow N2 gas flow is inevitable. Due to the limitation of surface locations, and in order to develop all field recoverable reserves, the only way is to drill wells in the highly active shallow N2 gas areas. The field is developed by drilling costly horizontal multilateral wells with maximum reservoir exposure. Wells typically start by drilling two large sized surface sections, a 28-in which extends to +/-160 followed by a 22-in wellbore sections. While drilling the 22-in section only extends to +/-1200-1800 ft, however, multiple drilling challenges have been observed as a result of the presence of a highly active shallow N2 gas formation. Gas influx while drilling, well flowing and gas channeling after cementing, and continuous gas bubbling in the cellar represent the main challenges experienced in the 22-in surface section. This paper will present details of the engineering analysis performed and the procedure developed to enhance well design and cementing through the highly active shallow N2 gas surface section.

Downhole tool failures induced by drill string vibrations was one of the leading causes of non-productive time in a deep exploratory field in southern Iraq. To improve drilling efficiency, it was paramount to understand the primary source of potential drilling dysfunction before commencing field development phase. To overcome the challenge, a finite element analysis (FEA) study was developed to simulate the drillstring transient dynamic behavior from bit back to surface. The model has been utilized to quantify the potential vibration, contact force, torque, displacement and other high-interest parameters of every drillstring component in the wellbore. To fully exploit the modeling algorithms, it is required to input a comprehensive dataset including mechanical rock properties, cutting structure design, bit drive mechanism, drillstring physical characteristics, 3D well profile and expected drilling parameters. Using offset well data, surface and downhole measurements, and a thorough knowledge of drilling equipment, the model creates a virtual drilling environment simulating the downhole drilling conditions enabling the evaluation of the source of inefficiency. Finally, the model is validated for its accuracy by comparing its outcomes with actual field acquired data. By accurately modeling the drillsting interaction with the drilling environment, the operating company was able to evaluate different BHA options to safely drill the wells and by reducing harmful vibrations, minimizing tool failures, increasing ROP, this translates to a reduction of drilling time by 24%. This paper will share with the industry a case study demonstrating the value of the utilization of the advanced dynamic modeling which has been able to save over 500 K$ per well to the operating company by an efficient selection and placement of drill string components. This approach has enabled to outperform past drilling performance and has become the norm in similar fields in southern Iraq.

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Obtaining a good cement bond is a continuous challenge, especially if the well being cemented is a high-pressure exploration gas well, and it is one of the very few gas wells drilled in the country. Poor adherence to the casing and the formation, channeling due to gas migration and microannulus are some of the main risks that could result in a poor cement job. Achieving zonal isolation and a good cement sheath protecting the 7-inch liner turned out to be an objective missed for the first two wells of the campaign, compromising the long-term supply of gas to the South region of Iraq. To solve the situation, it was necessary to implement something more than a mere cementing additive; it required a multifactor analysis with an experienced multidisciplinary team. A set of good drilling practices, proper drilling fluids, proven cementing techniques and new technology slurries were combined to improve the precious results. To obtain a sound cement quality log, the well engineering department teamed up with cementing experts, drilling fluids specialists, liner hanger company representatives and operations personnel. With effective meetings, proper risk assessment and visible leadership, the team generated a series of initiatives that included: drilling hydraulics optimization, mud weight selection, drilling practices re-definition, liner hanger procedure adjustments and cementing slurry design. As a result, the borehole caliper was significantly improved, the liner hanger allowed full rotation while cementing, cement returns were observed above the liner top after the job, no evidence of gas migration was observed and the CBL-VDL-USIT log showed a remarkable improvement in the two jobs where the engineering initiatives were applied. Being able to achieve a positive proof on cementing integrity, one of the most important acceptance criteria for the National Oil Company (NOC) regulation entity, enhanced the trust on the technical experts of the engineering team to deliver solutions of complex problems.