Use of horizontal well completion to enhance hydrocarbon recovery has increased considerably in the past several years. Projections for future horizontal wells hold considerable promise as long as well productivity enhancement outweighs the incremental cost. The success of horizontal wells to date appears to be related to the development and application of specific technology. Optimized completion techniques are on top of the list of such required technology. Recent publications clearly demonstrate that without proper formation evaluation, adequate completion is typically unachievable and often results in premature well abandonment.
This paper targets the three most common horizontal well formations subject to completion: naturally fractured, matrix permeability dominated systems and formations hounded by permeability dominated systems and formations hounded by a gas cap or an aquifer or both. The formation parameters that best define matrix permeability dominated systems are quite different than those associated with naturally fractured formations. The paper first identifies the parameters that best define individual formations. Possible completion options for these formations are then discussed
Optimized completion recommendations are presented for each of the formations through use of case studies. Recommended completion procedures for naturally fractured formations require use of external casing packers and alternating perforated or slotted and blank pipes. zonal isolation is of prime importance in matrix permeability dominated systems, especially when the pay interval is bounded by a gas cap or an aquifer or both. The recommended completion procedure for these types of formations uses cemented casing and selective perforating.
Enhanced hydrocarbon recovery of horizontal and highly deviated wells is not new. Examples of horizontal and highly deviated wells date back to the early 1940s. In the past decade, improvements in horizontal/inclined well drilling technology have renewed the interest in horizontal well completion. Concurrently, new technologies in the areas of formation evaluation, well performance, completion, testing and stimulation have been developed and applied. Production success, however, has been mixed in more than just a few basins. Success stories from the Austin chalk, the Bakken shale and Niobrara basins in the U.S., basins in central Alberta and reservoirs in central Europe to far east Asia have always been accompanied by examples of less-than-desirable results. The unsuccessful cases have one thing in common — significant reduction in hydrocarbon production once the well is put on production.
Horizontal and highly deviated wells have been in production for several years. The industry has accumulated production for several years. The industry has accumulated sufficient data to address the reasons for unusual production decline. Production decline can be the result of pressure depletion, communication with depleted zones, increased water production and initiation of gas coning. Proper completion and consideration of zonal isolation can eliminate a significant portion of these problems.
This paper demonstrates that appropriate formation evaluation is vital to proper completion and zonal isolation. The majority of horizontal wells completed thus far can be classified into three groups: those completed in naturally fractured formations, those completed in matrix permeability reservoirs and those completed in reservoirs bounded by a gas cap, an aquifer or both. The formation parameters that best define a naturally fractured formation are quite different from those associated with a matrix permeability dominated system. The logging and testing tools required also differ depending on the formation type. The difference in the measurement geometry between vertical and horizontal tool orientation further complicates evaluation.
This paper first discusses the essentials of horizontal well planning and the necessary measurements during drilling planning and the necessary measurements during drilling operations. Next, horizontal well completion options are discussed.