The understanding of salt beds has been significantly improved over the years; however, certain operational challenges still persist. Conditions encountered during drilling salt formations may lead to stuck Logging While Drilling (LWD) and or wireline tools, which, at times, can contain radioactive sources. As data gathering remains a primary requirement in exploration wells, cost optimization, beside risk mitigation, is a further challenge in today’s economic landscape. A holistic approach is proposed to address these main objectives. The conventional procedure required drilling and formation evaluation (LWD and or wireline) in the section above the interbedded salt formation, followed by rotary steerable (RSS) only in the interbedded salt formation sections of the well. Considering the shallow depths of the well and the proximity to the aquifers, the threat posed by losing radioactive sources in the well is significant, therefore, formation density and neutron porosity logging operation is often compromised due the inherent risk. Logging While Tripping, a method in which tools record open hole data from inside the pipe, resolves this compromise, as the risk of lost in hole (LIH) is virtually eliminated. The empty LWT collars are run in the last bit trip or reamer run, as they do not affect the drilling operation. Once the well’s total depth is reached, the LWT logging tools are pumped from surface, safely inside of the pipe, and data is acquired while tripping the drill pipe out of the well. If the situation is evaluated as risky, drilling operation may continue without data acquisition. In case the logging tools already were deployed, they can be retrieved at any time by wireline or slickline. Prior to the introduction of the LWT in the drilling/data acquisition procedure, only gamma ray - sonic data was acquired over the challenging formation sections. Compressional and shear data may be important to improve modelling accuracy; however, they may be negatively affected by various factors such as drilling noise, mud properties, washouts and gas in the formation, particularly reservoir rocks interbedded with thick salt beds. When compared to the Neutron-Density porosity, sonic porosity is noticeably inferior, showing limited formation signature. Neutron-Density porosity correlates well with core data.

The proposal of this paper is to share the case history and knowledge learned in this first application of the multistage zipper frac procedure and techniques in Biogenic wells. This breakthrough achievement was planned and executed by ADNOC Onshore Biogenic Drilling Department in Abu Dhabi which involves seven different services, each has a high importance and close collaboration was a key contributor to the feasibility of the project and the collective success obtained. The Zipper frac method selected and tailored by the Biogenic Team for the specific application enables to significantly increase the number of fracs per day performed over 2 wells. This technique stages multi-well completions, where wells are completed in a back-and-forth manner. One well is being pumped /fractured while the other well is being plugged and perforated for next stage. One of the key achievements in the Biogenic Zipper frac operation lies in the easy switch from line to another by using a manifold in a safe manner and without confusion. Because of the focus and high potential of Biogenic gas, Biogenic Team faced the challenge of delivering the two wells on a very tight schedule. This led the Team to review, select and implement a novel methodology that would deliver time and cost savings to the Project. New ideas were scouted and analyzed by different departments and service companies to select the most appropriate. Upon selection of the zipper frac method, meetings were done to issue and finalize a proper implementation plan for this multi-frac operation, which was a first in ADNOC Onshore. Explaining in workshops to key stakeholders and respective higher management the methodology and plan as well as the associated savings was essential to get full support and endorsement for implementing this method. There was no doubt that this method was the best way to achieve the goal with the tight given timeframe. Successful implementation resulted in of around 50 days savings compared with applying the conventional multiple frac procedure / method on a well-by-well basis. Wider application of this method represents a breakthrough in delivering future fracked wells cheaper and faster thereby bringing significant savings to future Biogenic gas development projects. Because of the importance of ongoing assessment and potential future development of Biogenic gas and unconventional resources, sharing details of ADNOC Onshore first implementation of the Zipper frac methodology is of benefit to the industry. The detailed account of its implementation (inclusive of added important technical features such as dissolvable plug and perf technology) that has delivered safely and successfully twenty-four (24) staged fracs in a short time frame represents a piece of useful knowledge.

Over the last 60 years, Abu Dhabi, United Arab Emirates (UAE) has been producing oil and gas from different conventional fields. Nowadays, and as part of the State long-term strategy to achieve the nation objective of gas self-sufficiency, it has been decided to explore, appraise and develop unconventional plays in the Northern area including the construction of early production facilities to supply the gas power plants. Three wells were drilled as part of the first phase of the project; consisting of a pilot hole into an extremely heterogeneous formation; two of them were horizontalized into the targeted formations. The first well across the salt represented a tremendous challenge due to limited rig capacity generating hole stability issues that required unplanned remedial jobs. The second well was deviated across the salt as pilot hole, then side-tracked and horizontalized in the targeted reservoirs. The third well was drilled directly as horizontal lateral based on previous lessons learned validating the horizontal concept for the future field development plan. The exploration phase constituted by these three wells, were drilled and completed successfully. A detailed data gathering program was executed allowing mapping of the area validating the presence of gas. The drilling parameters, such as rate of penetration (ROP) for the horizontal section was enhanced by optimizing the drilling Bit design. The mud logging results have confirmed the extremely heterogeneous formations across this section allowing determining the most fit for purpose bottom hole assembly (BHA); obtained after a detailed optimization process. Multiple lessons learned were captured and immediately applied leading to a significant reduction on total days per well that reflected on an outstanding cost reduction including rig move optimization, incrementing the overall efficiency of the operations. This project has proven the potential of unlocking the development of this field focusing on the targeted untapped reservoirs. Key unprecedented achievements have been fulfilled during the execution of this phase of the project: 1. First time to drill across a salt dome in Abu Dhabi Emirate 2. First time that horizontalization has been applied to the targeted formations. In addition, a better understanding of the optimum drilling parameters for future phases has been obtained.