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.
Alkaline Surfactant (AS) flooding is an enhanced oil recovery (EOR) method to mobilize residual oil. Deatailed understanding of transport during these recovery mechanisms requires detailed pore-scale studies. This point leads to the utilization of X-ray imaging for its application in pore-scale characterization. Synchrotron-based X-ray imaging is an advanced technique that is capable of capturing the dynamics of pore fluids at the microscopic scale. The aim of this project is to investigate the pore-scale flow of AS flooding at two different salinities in carbonate rocks using real time 3D images collected by synchrotron-based X-ray imaging. The morphologies of the non-wetting phase are first computed, and oil recovery in the two scenarios is estimated. In addition, the wetting states of the two conditions are assessed by contact angle measurements. It was observed that optimum, or Winsor type III mobilized more oil, since it yielded a higher recovery value, as compared to under-optimum or Winsor type II-. Alkaline surfactant at optimal salinity was marked as an ideal condition that effectively reduces interfacial tension (IFT) to mobilize residual oil. This study provides insights in the pore-scale flow mechanisms that occur during AS flooding, which are important for understanding the basic EOR mechanism of this particular flood.
Quantifying anisotropic rock properties from sonic data is a well-known approach that has many applications. For instance, the percentage sonic anisotropy in the formation provides vital knowledge when constructing Geomechanics mechanical models and when determining optimum well trajectory for horizontal wells. One of the main outputs from sonic anisotropy processing is the fast shear-wave polarization azimuth (FSA) derived from auxiliary tool orientation measurements included in the tool string with the sonic tools. This FSA is polarized along the direction of fracture strike, in case of fracture-induced anisotropic zones, and /or along maximum horizontal stress, in case of stress-induced anisotropic zones. When the hole shape is oval in one axis by breakouts and in gauge in the other axis, the sonic tool remains oriented in one direction throughout logging intervals. As a result, the fast shear azimuth will be stable in one direction. This locked direction inherently has a 90° ambiguity if interpreted wrongly particularly if no borehole image data were available to validate this direction from the strike fractures or breakout directions. The main objective of the study in this paper is to validate the direction of FSA, and then horizontal stress orientations, from sonic data in vertical wells when the sonic tool keeps a singular orientation throughout the logging and no borehole image data are available to support the direction of horizontal stress orientations. This validation is represented through a graphical interpretation of the FSA, both qualitatively and quantitatively, at intervals that exhibit stress-induced anisotropy and without assist from borehole image interpretations. Three examples are presented in this paper. The first one shows a determining of the maximum horizontal stress from the graphical interpretation of FSA after processing the sonic data. This interpretation is validated with image data. The other two examples are from wells where only sonic data is used to determine the horizontal stress orientations using the FSA graphical technique
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