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Abstract
Thorough planning of a well, or better yet, a field, to determine how each well can provide maximum production throughout its lifetime is unquestionably very important to the operator. For fields of vertical wells, this process is well understood. For horizontal completions, however, only 20 years of practice are behind us. For lower permeability reservoirs, the theory that using horizontal wellbores can eliminate fracture stimulation has proven to be false. Today, the assumption that moderate to higher permeability reservoirs will never be candidates for stimulation is also being challenged by a high number of non-economic wells. Too often, we find many of these horizontal completions need stimulation but are not candidates because of the mechanical limitations of the completion plan.
This paper discusses the many field and reservoir aspects, including formation geology and localized tectonics, that can influence proper well placement for future applications of fracture stimulation. The evaluation of emerging completion tools and processes that enable fracture stimulation should be nurtured to allow wells in less promising areas of the reservoir to become economic contributors and not net losses on the ledger. These wells must be incorporated into the general recovery plan for a field and taken into account in completion schemes (especially perforating techniques) to best produce the well when stimulation is not required, yet keeping stimulation as a future option. Different completion schemes may have to be used based on the position of the well within the field. Field experience with supporting data will be presented and discussed in depth, as well as conventional and new stimulation options that would optimize the specific applications.
Introduction
We all have to admit that we try to blame the inabilities of “Mr. Foresight” and trust “Mr. Hindsight” who is always correct. Sadly, many of our attempts to look through the technological crystal ball fail miserably. Unless a time machine is invented, the notion of getting a 20/20 foresight may result in a 50/50 failure rate, e.g. flip of a coin (excluding double headed coins). Obviously, whoever dug the first 800-ft oilwell in China in 347 A.D.1 was totally unaware that it might need stimulation in the future. Even after the tight oil sands in Pennsylvania were stimulated using explosives in 1860,2 oil operators might not have realized that acid would one day be used to stimulate production of oilwells, as performed by the Ohio Oil Co. in 1895,3 or even that fracture stimulation would be performed by pumping fluid in a wellbore (done in 1949).4
Looking back, however, we know that “Mr. Hindsight” is not perfect, either. Claims that Col. Edwin Drake drilled the first oil well in 18595 could be discredited quickly by the aforementioned well in China; and even when we only consider wells in the U.S., the Thoria-McKee well was drilled in 1814 in Ohio.6 Mr. Ranney’s claim as the first creator of horizontal wellbores in 19397 is equally incorrect since the Department of Energy (DOE) marks the completeion’s birthdate as 1929 in Texon, Texas. Mr. Ranney, however, could mark his well to be the first multilateral well where one lateral branches off another lateral. The latter lateral was stimulated using TNT. Note that multilaterals branching from vertical wells were completed as drainholes by Eastman and Zublin in the mid-1930s.8
What are the common denominators of these inconsistencies? They are length of time, lack of communication, and limited engineering knowledge. In this modern era, communication is definitely no longer a problem. However, in regards to horizontal well technologies, length of time and our technical knowledge is considerably limited when compared to vertical well experience. In the U.S., for example, there are well over 350,000 vertical wells in Texas alone9; whereas, horizontal wells in the whole U.S. total less than 4,000 (less than 14,000 worldwide). Most of these horizontal wells were completed after 1990. Prior to 1990, U.S. horizontal wells totaled less than 300.10 It is probably these wells that have depleted to an unsatisfactory production level, making stimulation a necessity. And, as we know now, stimulation technology and concepts have changed.
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