Method for developing oil or natural gas shale or tight rock formations in two step process |
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申请号 | US14560763 | 申请日 | 2014-12-04 | 公开(公告)号 | US20160160625A1 | 公开(公告)日 | 2016-06-09 |
申请人 | Tim Maloney; | 发明人 | Tim Maloney; | ||||
摘要 | A method for developing oil or natural gas shale or tight rock formations by constructing wells in a two step process. The method includes an algorithm for determining under what conditions this two step process is the preferred option for developing a shale or tight rock resource. Step one is to drill a multilateral well with a profusion of unstimulated open-hole laterals from a main wellbore, after which the well is produced for a period of time. Step two is to re-enter the well and install a multistage hydraulic fracture completion. The method includes drilling the main bore and laterals in a specific sequence and geometry to facilitate running a frac liner in the future when the multistage fracturing step is carried out. | ||||||
权利要求 | What is claimed is: |
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说明书全文 | The present invention relates generally to the recovery of subterranean resources, and more particularly to a method for enabling commercial production of oil or natural gas from tight rock formations. Subterranean deposits of shale or tight rock that contain natural gas or oil are assumed to require hydraulic fracturing during the original drilling in order to create sufficient contact surface area and flow paths to enable production of commercial quantities of hydrocarbons. However, in certain planned or unplanned cases, these same formations have been drilled and put on production before the wells were hydraulically fractured. In some of these cases the wells produced substantial quantities of oil and/or natural gas prior to hydraulic fracturing. These wells already had the expensive equipment installed required for hydraulically fracturing, but the fracturing was delayed for either reservoir evaluation purposes or mechanical problems, thus preventing the fracturing at the time of original drilling. Even so, the quantities of oil or gas produced from these wells were deemed insufficient to economically justify drilling more of these type of unfractured wells. There are three reasons for this: 1) the wells were drilled to optimize the performance of the hydraulic fracturing (not for an unfractured well in shale/tight rock), 2) the capital cost included the downhole equipment for fracturing (thus requiring higher oil/gas flow rates to meet economic hurdles), and 3) the flowrates from these unfractured wells did not have the high initial peak rates associated with hydraulically fractured wells (on the other hand, the decline rates in these unfractured wells were not as severe as the fractured wells). So, if the economics of an unfractured multilateral well can be improved by drilling it to optimize its unstimulated flow capacity and by not installing the expensive equipment for fracturing at the outset, then these types of wells have a place in the overall development of shale or tight rock formations under certain conditions. In the United States when developing onshore shale or tight rock oil or natural gas resources the normal practice is for the operator to lease the minerals from the mineral owner with a 3 to 5 year period in which commercial production must be established in order to hold the lease. If commercial production is not established within this time, then the lease expires and the operator no longer has access to the minerals. This practice is a carryover from conventional onshore oil and gas developments in which the fields are much smaller in overall acreage and the construction of the infrastructure facilities needed to support the drilling campaigns can be completed within this time frame. However, in most shale or tight rock plays the overall acreage positions are much, much larger, so these individual lease timeframes (3-5 years) are often out of sync with the time to complete the supporting infrastructure projects (pipelines; batteries; oil, water and gas processing plants; and public infrastructure [roads, bridges, power transmission, water, human resources, etc.]. This disconnect between the timing of individual leases and infrastructure projects causes additional costs and inefficiencies for operators because they rush to build whatever infrastructure they can to handle the wells being drilled to avoid lease expirations, only to go back and redo much of this infrastructure later as the play matures and the ultimate size and volumes are better understood. So, a two step process where leases are initially held by drilling lower cost unfractured wells could help sync up the timing of the subsequent hydraulic fracturing step with the completion of the supporting infrastructure projects. This could improve the overall economics of the entire play by helping to right size the infrastructure projects and to conduct the hydraulic fracturing step in a more orderly and efficient manner. The present invention provides a method to drill an oil or gas well in a shale or tight rock formation in a two step process, first as an unfractured multilateral well, and later, re-entered and completed as a multistage hydraulically fractured well. The method is designed to optimize both the initial unfractured multilateral well and the future multistage fracture completion. The initial unfractured multilateral well is optimized by drilling numerous side laterals as quickly and cheaply as possible to effect the maximum reservoir contact surface area at the lowest capital cost. The future multistage completion is optimized by having a main wellbore with high integrity to allow the frac string (liner, swell packers, frac sleeves) to be run smoothly and for the isolation swell packers to be set securely between the side laterals, thus enabling a multistage hydraulic fracturing job to be performed successfully. Hence, a key feature of this method is to drill the side laterals quickly and cheaply, but to ensure the main wellbore is smooth, straight and to gauge. One embodiment of this method is depicted in the figures and is described below. This embodiment shows a drilling sequence from heel-to-toe, in which the main lateral is drilled out in individual steps, each one made up of a short straight hole section and then backing up to perform the side lateral kick out in either direction. These side lateral kick outs can be made with various directional tools which direct the drill bit in a combined sideways and upward orientation so that the main wellbore remains the straight bore ready for the next deepening step. Once the side lateral has made most of its turn away from the main wellbore, it will continue to be drilled within the targeted zone for the intended distance. After which the drilling assembly is readied for the next short straight section. Given the importance of maintaining a smooth main wellbore, the side laterals are drilled in such a way as to not unduly damage the main wellbore. This can include, for example, not attempting to re-enter a side lateral if it would create excessive wash-outs in the main wellbore. Hence, when drilling problems prevent one of the side laterals from reaching its intended distance, it would be left that way and the drilling would proceed on to the next section. In order to prepare for the future frac string installation the main wellbore is cleaned with at least one wiper run and, if any wellbore damage is suspected, a log is run to identify where the good and bad sections are located. This will allow the swell packers to be spaced along the frac string so that they are set in gauge hole sections. During the second step, when the well is re-entered and prepared for multistage hydraulic fracturing, it will similarly begin with gauge and wiper runs to ensure the main wellbore is clean and able to accept the frac string all the way to bottom. Once the frac string is run and the swell packers have set, then the multistage fracturing treatment is carried out. In addition to these technical components, the method includes an algorithm for determining under what conditions this two step process is the preferred option for developing a shale or tight rock resource. A figure of a flow chart is used to describe one embodiment of a decision process an operator can follow in determining when to apply this two step well type. For a more complete understanding of the present invention and its advantages, reference is now made to the following description taken in conjunction with the accompanying drawings, wherein like numerals represent like parts, in which: Referring to On the right column of |