Showing papers by "Abu Dhabi Company for Onshore Oil Operations published in 2014"

Mechanical Layering: Implications for Hydraulic Fracturing in an Unconventional Tight Carbonate Reservoir in Abu Dhabi, UAE

Abstract: The tight-carbonate gas reservoir of Onshore Abu Dhabi, UAE, is characterized by having alternating thin and dense reservoir and none-reservoir units, where hydraulic fracturing is the most effective way to increase the productivity by creating the maximal areal contact with the wellbore. The most significant operational constraint associated with hydraulic fracturing is the containment of the produced hydro-fractures, which might extend beyond the reservoir units. To avoid this problem, which is a function of the mechanical and elastic properties of its reservoir rocks and the type of existing stress regimes, these attributes within the reservoir units and the surrounding cap-rocks should be understood. The 1D Mechanical Earth Models (MEMs), which involve constructing the three principal in situ stresses’ profiles with depth together with the elastic and strength properties of the tight carbonate units with their cap rocks have been carried out using different data along 12 wells such as sonic logs, full-bore microimage(s), and rock mechanics testing. The results of these twelve 1D MEMs in the field indicate that the three principal in situ stresses’ axes swap directions and magnitudes at different depths giving rise to identifying different mechanical bedrocks with different mechanical properties corresponding to different stress regimes (normal and strike-slip) at different depths. The implications of these results suggest that it is likely that the produced hydraulic fractures are mainly vertical to subvertical under both normal and strike-slip stress regimes. Further, depending on the stress regime, the propagation of the hydraulic fractures would likely be into the horizontal in case of strike-slip regime compared to vertical propagation within the normal stress regime. Further, longer hydro-fractures are expected to be developed in stiffer layers.

Wireline Straddle Packer Microfrac Testing Enables Tectonic Lateral Strain Calibration in Carbonate Reservoirs

Abstract: Wireline straddle packer microfrac tests have become an important technology in creating microfractures to measure in-situ formation breakdown pressure, fracture re-opening pressure, fracture closure pressure and stress contrast between reservoir and non-reservoir intervals. The formation tensile strength can also be estimated from the difference between breakdown and re-opening downhole pressures. This case study describes the use of microfrac tests measurements to validate and calibrate the horizontal stress profile in various intervals of the carbonate reservoir. Well-injection plans, cap-rock integrity assessment, shale reservoir fracture containment, stress contrast and minimum and maximum horizontal stress estimations can all be quantified from microfrac test measurement. Six straddle packer stations were tested for microfracturing in this study well. One microfrac test was repeated in one formation due to observed poroelastic effects in the fracture re-opening pressure responses. Poroelastic effects around the borehole occur when the pore pressure near the borehole increases with the injection cycles, thereby making it more difficult to effectively re-open the pre-existing induced fracture. When poroelastic effects are evident, it is important and recommended to record the first pressure fall-off cycle after the formation breakdown for fracture-closure identification. Subsequent cycles will indicate higher fracture closure pressures and therefore overestimate the minimum horizontal stress in the interval. This paper describes the pre-job modeling, real-time monitoring and post-job interpretation of straddle packer microfrac testing for recalibration of the geomechanical model to provide continuous logs of in-situ horizontal stress profiles over the entire interval.

8.1.1 Strategic Water Reserve's effect on the water supply system in Abu Dhabi: A System Dynamics Approach

Abstract: The Emirate of Abu Dhabi relies heavily on desalinated water as a water resource as it is the main source of municipal water. However, desalination is vulnerable to seawater pollution or emergency breakdowns. Therefore, reservoirs of a substantial capacity are needed for water supply under contingency, since existing water in storage and the water network can sustain maximum of two days of water demand in Abu Dhabi. The government has introduced Artificial Storage and Recovery (ASR) as part of Strategic Water Reserve program. This paper studies the effect of ASR on the current water supply system using system dynamics approach. As a result of the simulation, ASR can delay the appearance of the first water shortfall by 2 years and 9 months. Under uncertainties of red tide incidents and demand seasonality variation, Monte Carlo simulation analysis shows that the first water shortfall will be delayed by two and a half years at 97.5% confidence level than if no ASR is in place.