Saudi Aramco's Ghawar Field is a massive carbonate reservoir with sub-zones of varying reservoir quality and has been under flank-water injection. It is a complex reservoir, with thin super permeability layers (10 feet) that are generally stratiform and in some cases fractured, associated with high productivity. Laterally extensive super permeability beds, in good vertical communication with the rest of the oil bearing reservoir, can significantly increase both well productivity and sweep efficiency. However, isolated super permeability layers can cause early water breakthrough, which adversely affects oil recovery as well as increases the field operational cost. Furthermore, large permeability contrasts can complicate effective drainage of lower porosity zones in the lower part of the reservoir that contains about 35 % of the original oil in place. For this field, pressure and saturation monitoring have been key factors in achieving the overall reservoir management objective of maximizing recovery at the lowest cost. Saudi Aramco is currently surveying the key new wells drilled behind the flood front using the multi-probe formation tester for obtaining pressure measurements, performing interval tests, and taking fluid samples along the well-bore. The primary objective of the surveys is to establish whether the super permeability beds as well as the lower porosity zones are introducing differential pressure depletion, which will directly impact the field's completion and production strategy. Obtaining fluid samples across the reservoir zones is also a key part of the surveys, to establish water salinity and movable oil fraction in zones with breakthrough where the injection and formation waters are mixed. Determining the fraction of movable oil in the lower porosity zones, where the conventional open-hole log results are uncertain, is very crucial in optimizing recovery. It is also a powerful method to evaluate the sweep in the lower zones matrix where the diffused fractures density is higher and assist the dynamic interaction between the two systems. The on-going Uhawar Field monitoring has shown that there is good vertical communication in the higher quality zones, at the top of the reservoir and embody the super- permeability thin beds. However, local and reservoir scale barriers as well as differential depletion has been observed towards the base of the reservoir. These barriers have resulted in poor sweep efficiency with zones containing bypassed oil. These zones are now being targeted by dedicated dual vertical-horizontal completions. In this paper, we show that the pressure and saturation monitoring integrated with other dynamic and geological data contribute immensely to obtain the best completion for optimizing oil production and recovery. Furthermore, we also show that in areas of good vertical communication, super permeability is advantageous to the field development, due to its high productivity and large drainage area exposure. P. 111
This paper addresses the successful isolation of a loss circulation zone of a short radius horizontal completion utilizing the cement retainer technique in a highly fractured environment. The process was applied to a well in a highly fractured carbonate reservoir undergoing pressure maintenance by water injection. Fracture orientation in the area is running mainly NE/SW. While drilling the horizontal section, complete lost circulation was encountered in the middle of the planned lateral section, most probably through a fracture. Circulation could not be regained by pumping LCM pills or placing cement plugs. The horizontal section had to be plugged and a new horizontal lateral was drilled in a different direction. A drillable squeeze packer was used to hold a good kick-off cement column above the loss circulation zone. Prior to the workover, the well was producing 3.3 MBOD at 47% water cut. The initial post workover test showed 3.0 MBOD restricted (choked) water-free production. Introduction The main objective of applying the horizontal drilling technology is to realize a greater economic benefit through increased well productivity by enlarging the area of contact with the reservoir rock at reduced pressure drawdown. Horizontal wells can offer significant economic as well as recovery benefits when properly applied. Increasing the production rate reduces the operating cost and thus increases the rate of return. In addition, horizontal drilling reduces the number of wells needed to deplete an area. Another benefit of horizontal completions is the diminished risk of water coning due to the lower drawdown in the wellbore. It also improves the areal and the vertical sweep efficiencies. On the characterization side, the horizontal technology improves the information gathering process. Horizontal drilling have proven that formations are more heterogeneous in the lateral direction than indicated by the vertical wells. Failures in horizontal drilling are mostly attributed to inadequate reservoir characterization and poor site selection due to lack of petrophysical data. Planning for a horizontal well includes a thorough review of, but not limited to, reservoir performance, reservoir geology, fracture presence and orientation, permeability anisotropy, well pressure transient testing and well logging. Most of this data are available since horizontal applications are development rather than exploration. Fractured reservoirs are mostly targeted for horizontal drilling. However, as in this case, the fracture systems presented the challenge. Background Horizontal drilling technology was first introduced in the Arab-D reservoir in Ghawar Field in 1994. Initially, the main objective was to deplete thin oil column areas while minimizing water production. The area the well was drilled in is highly swept. There are wells producing at 72% water cut or higher. The average water cut in the area is about 45%. Several workover techniques were tried to control water production, from through-tubing bridge plug isolation to polymer treatment. When successful, these techniques reduced water production only temporarily. In the field, produced water is treated and injected back in the reservoir through water disposal wells. It is imparative that a better way is needed to control water production to cut cost and injection volume when neccessary. Horizontal drilling is one choice.
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