Case History: Integration of Rock Mechanics, Structural Interpretation and Drilling Performance to Achieve Optimum Horizontal Well Planning in the Llanos Basin, Colombia, South America. Abstract The productivity enhancement associated with horizontal wells through reservoir intervals makes them an attractive option for improving overall field economics. However, the implementation of a first well of this type in an area requires careful planning if operational and commercial success is to be ensured, particularly if there are known geological and/or drilling difficulties. This paper describes the approach taken by ECOPETROL, the Colombian State Oil Company, to optimise the planning of the first horizontal well in the Llanos Basin, in a field some 50 km East of the tectonically active Eastern Cordillera of the Andes in Colombia, South America. Introduction ECOPETROL were planning to drill a horizontal well in the APIAY Field of the Llanos Basin in Colombia (Fig. 1). The well, GUATIQUIA 3H (G-3H), is needed to drain the reservoir sands in a structure trending approximately N20E in an area (Fig. 2) where there was no previous experience of drilling high angle or horizontal wells. Examining all aspects of the challenge associated with completing this well was essential if operational and commercial success was to be ensured. Recent experience has shown how difficult drilling in the nearby foothills can be, even in vertical wells. Hole instability there has been severe, and in general horizontal holes pose additional risk. Given the similarity of the rocks in the APlAY area, the troubles encountered in drilling the off-set vertical wells, and the potential similarity in the stresses, there had been conjecture that G-3H could not be drilled. With this background. ECOPETROL decided to commission an assessment of the rock mechanical and hole stability issues that were likely to impact the drilling of the well. From a reservoir management point of view, the direction and length of a horizontal section through the pay zone will usually be selected on the basis of optimising overall reservoir performance. This will include considerations' such as the geometry of the structure, maximum drainage area and potential interference with the drainage pattern of other wells. These are clearly very important issues which directly impact the economic assessment of the well. Indeed, based on reservoir simulation and the proximity to existing surface infra-structure. the early conceptual designs had the proposed G-3H well being drilled from the south along the crest of the structure (N20E). However, integration of reservoir engineering considerations with potential drilling and completion difficulties may prompt the need to compromise to reduce overall operational risk. Wellbore Stability Considerations Wellbore instability can lead to drilling difficulties such as lost circulation where tensile rock failure has occurred to spalling and/or hole closure in the case of compressive rock failure. In severe cases hole instability can lead to stuck pipe and eventually loss of the open hole section. Conventional wellbore stability theory shows there are many factors that are likely to influence the competency of the wellbore wall, including formation pressure, depth, formation strength, stress state, mud weight, mud cake efficiency and time. Furthermore, the theoretical impact of well trajectory with respect to stress orientation is well understood, and demonstrates the need to carefully consider the well trajectory when planning high angle or horizontal well sections. Formations are generally subjected to stresses derived from the weight of the overburden rocks, and any regional tectonic loading that exists. The stresses can be resolved into three principal components. which in most cases are the vertical, minimum horizontal and maximum horizontal stresses (Fig. 3). In passive sedimentary basins such as the North Sea the vertical stress is usually considered to be the largest (Fig. 3a). P. 359^

Conformance technology is the application of processes to reservoirs and boreholes to reduce water production, enhance recovery efficiency, or satisfy a broad range of reservoir management and environmental objectives. An operator desired to isolate aquifer zones and reduce water production in a horizontal section. First discussed is problem identification in the oil producing well; following, the application of reservoir simulation to determine the amount of and the most appropriate treatment application is discussed. Depending on fluid density differences and wellbore deviation, conventional conformance treatments can tend to slump/rise along horizontal or highly deviated sections, compromising the placement accuracy and overall treatment success. The stress-dependent (thixotropic) rheological properties of the conformance technology service used in this project provides rapid viscosity increase during placement, allowing the treatment to remain in place until in-situ crosslinking occurs at a predicted time, helping to provide a competent seal across the targeted area. A reservoir simulator was used to optimize the design of a conformance treatment and to evaluate the efficiency of the conformance solution. During pumping of the conformance system for the isolation of the lower zone because of water problems, it was observed that the entrance of the two sealing systems to the formation increased the pumping pressure, showing the sealing effect. Additionally, the thixotropic characteristic of the conformance sealant could help keep the systems in place until they acquired the consistency to complete the isolation of the water zone. Water production after conformance treatment was reduced by almost 65%, aligned to the expected results from diagnostics. A successful conformance operation was completed in a horizontal section, overcoming the natural tendency of standard fluids to slump/rise along horizontal or highly deviated sections. The proper conformance diagnostics with a reservoir simulator was vital to the success of this project.

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Global warming is one of the most serious environmental, social and economic threats currently facing the planet, so many companies and organizations have generated a strategic approach to combat it. One of the most efficient strategies is the reduction of energy consumption, which not only positively affects the reduction of fuel consumption, but also shows improvements in both financial and technological efficiency. This project allowed to create an analysis methodology applicable in the oil and gas industry, in whose process of analysis, important alternatives for optimization of energy consumption are detected, which contribute to the Greenhouse Gas Emission balance (GHG), a fundamental theme of Sustainability Worldwide. This methodology was applied in the field of higher production of hydrocarbons currently in Colombia, whose energy consumption is significant at the national level. The methodology included activities to measure energy consumption per well, coupled with a rigorous financial analysis that allowed the evaluation and selection of candidate wells for different optimization actions. As a result, technically applicable actions were obtained for the reduction of energy consumption, which were classified under an analysis of expected net present value and investment efficiency.