Production of shallow gas has presented a unique opportunity to implement a fit for purpose fracturing workflow due to the level of complexity these reservoirs present. Initially acquired logging data including open hole logs, mud logs, wireline pressure measurements and reservoir sampling as well as micro-frac readings confirmed the presence of relatively shallow gas in low permeability rock. Hence introducing fracturing as a favourable method of extraction made it imperative to address the level of complexity within the reservoir, which varied from the presence of anhydrites, extreme heterogeneity, water sensitivity, as well as the fault environment at such shallow depths. Exploring pilot holes and running advanced image logs as well as acoustic measurements along with micro-frac operation, provided critical data for completion design improvement to not only enhance the chances of successful placement, but also increase the overall gas output. The relatively low bottom hole static temperature and pressure, soft rock, heterogeneity and overall immaturity of the reservoir required extensive core flow tests. X-Ray Diffraction (XRD) as well as lithology scanner logs were also used to fully understand the complex mineralogy. A suitable salt tolerant fluid was proposed for fracturing before optimisation as well as the inclusion of fit for purpose acid systems. The workflow also utilised the extensive geomechanical datasets for analyses, as well as incorporating the geological and petrophysical interpretations. This was followed by sensitivity analyses of the fracturing design based on size of stages, stage spacing, cluster spacing, as well as the cement quality. After performing micro-fracturing tests, a one dimensional mechanical earth model (1D MEM) was optimised to enable better understanding the fracture geometry. The workflow also included the use of chemical tracers to qualify the success of each fracturing stage within the target horizontal section. The workflow started with a collaboration between geology, geomechanics, petrophysics, reservoir, as well as stimulation domains, which resulted in the completion of the first horizontal multistage fracturing completion within the targeted shallow gas reservoir. This milestone provided insight into the required planning for future gas wells within the region and has left significant potential for optimisation given the complexity of the reservoir. The consolidation of a workflow to deliver the first shallow gas project in order to extract the initially confirmed gas presence has presented a novel approach to such a niche project. This was initiated by utilising a time-lapse image analysis, petrophysical and reservoir evaluation, and then coupled with the introducing propped fracturing and matrix acidizing to further calibrate log-deduced parameters. A high level of detail in core analysis, as well as micro-fracturing interpretations, have reduced the uncertainty regarding fracture generation, initiation, and fracture extension into the far field in such a shallow and unconsolidated, low temperature and pressure reservoir.

This paper describes the frame work and new concepts implemented for appraisal data gathering from two undeveloped green oil fields (Fields-A and B) as shown in Figure-1. Acquired data program was a heavy schedule, involved testing of multiple wells, integrated by different teams to full fill all requirements which are vital for field's development. Limited resources, HSE and environmental issues, remote/ unmanned areas, heavy testing facilities, rig & rig-less resources and difficult topographic nature of these areas are part but not all of the challenges faced to implement the appraisal data gathering program to achieve the program objectives. An integrated workforce team was formed from different disciplines, project partners and all stakeholders succeeded to set an innovative scope of work, plan, procedures and distribution of responsibilities for each partner to overcome and trouble shoot these problems. The appraisal data gathering approach resulted in completing the appraisal program successfully as per the time line plan, obtained high quality of huge data, adhering to high safety operating procedures and standards at economic value.One of the major challenges was to avoid flaring of oil and risk of transporting huge quantities of crude oil produced during the long term production testing operation & risk of exporting by trucks to far locations at distances of around 130 Km from the source to store in other wells. Water handling during the injectivity test was also a big challenge. Safety operation related risk of high vapor pressure and flash point either in testing facilities or while loading and transportation in high temperature. H2S and SO2 are other issues. Proper planning, team work, risk assessment and mitigation plans, responsibility allocation the appraisal project was successfully completed in shorter time than expected and all objectives were met and obtained Shareholders gate approval to proceed with fields development in cost effective manner without any hazardous or fatalities.

The petrophysical evaluation for Sabkha environment is very challenge due to high reservoir heterogeneity and complex mineralogy in addition to existing of multi-lamination that have various thickness ranging from 1 to 20 ft., also these kinds of reservoirs normally have very high formation salinity that impact as well the water saturation calculations. In 2018, a unique worldwide biogenic shallow gas reservoir was discovered in Onshore Abu Dhabi, UAE in Miocene Sabkha deposits while drilling a dedicated well for deeper reservoir, the average reservoir gross thickness is about 4500 ft. with hundreds of intercalations from Clay, Limestone, Dolomite, Marl, Anhydrite and Halite. This paper presents the detailed challenges for such reservoir regarding the petrophysical evaluation (including but not limited to porosity calculations, water saturation evaluation by different methodology, net to gross ratio, log and core data integration, definition of high potential spot for testing, etc..) Moreover, the way to manage and mitigate these challenges in addition to testing technology and results. So far Five dedicated exploration wells were drilled in this reservoir at which a complete set of logs were acquired in addition to collecting of core footage about 4560 ft. from two wells and analysis is ongoing, also Rigless testing was done for 3 wells. In general, based on collecting data the reservoir properties showed very tight reservoir (permeability < 0.01 md) with high mineralogy complexity as well as high formation salinity (+ 300 kppm). Good Total Organic Carbone is also measures across the reservoir that confirmed the ability to produce Microbial gas. As a results of the integrated study, the sweet spots across the reservoir were identified and tested, accordingly placement for horizontal development wells as well as stimulation technology are optimized

Plan, drill and complete pioneer water disposal wells within the challenging Pilot Project of the complex unconventional reservoir and obtain approval, based on technical justification, of water reinjection within the Gachsaran Formation. This will exclude handling the additional manpower on a daily basis for managing water trucking operations day and night over the remote terrain to the nearby fields (90kms and 110kms). Consequently, this will reduce OPEX and extra liabilities incurred by HSE risks. The Project included five horizontal producers, completed for the first time within the Middle Gachsaran in the UAE's history. The expected field water production rates were 5000 bbl/d. There was no previous test data available to estimate the injectivity potential of the formation for water disposal. Additionally, no previous approvals were available from the HSE or the risk management team. Available G&G data and subsurface understanding were utilized to best optimize the water disposal wells. Potential reservoir zones were identified based on the good porosities with moderate permeabilities, vertical barriers and their confirmation through MDT pressure measurements, water intake information based on PLT results at nearby vertical wells, and reservoir connectivity. Subsurface and surface locations were finalized as near as possible to the pilot project facility to efficiently inject the water and reduce the CAPEX without compromising the subsurface targets and well integrity. The reservoir monitoring plan for the project was established to monitor any chance of vertical percolation of waste water in the shallow aquifer to avoid contamination. Multiple vertical barriers exist within the Gachsaran Formation with a regional seal that exists at 1850 ftTVDSS. The regional vertical seal exists at around 2000ft above the top of Middle Gachsaran. Therefore, there was rarely any chance that the injected water would communicate with the shallow formations. In brief, no vertical communication has been confirmed so far across the Gachsaran Formation within the Project Area based on the existence of vertical barriers (anhydrite beds-seals) and results of the formation pressure acquired at several wells and well test data in the area. The reservoir monitoring plan will allow us to overcome any possible chances of cross flow through cement behind the casing of the water disposal well to avoid shallow aquifer contamination. HSEIA / HSE (Safety) Case / HSE Studies Regulatory approval was successfully acquired. A test case to ensure the Middle Gachsaran as a water disposal candidate within the area. The reinjecting of produced water will save tremendous OPEX for full field development. This will create opportunities for new exploration blocks within this area to allow water disposal produced from deeper reservoirs. Consequently, we provide an attractive economic option to the overseas companies exploring deeper targets within this area.