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Introduction Tight gas is the term commonly used to refer to low permeability reservoirs that produce mainly dry natural gas. Many of the low permeability reservoirs that have been developed in the past are sandstone, but significant quantities of gas are also produced from low permeability carbonates, shales, and coal seams. Production of gas from coal seams is covered in a separate chapter in this handbook. In this chapter, production of gas from tight sandstones is the predominant theme. However, much of the same technology applies to tight carbonate and to gas shale reservoirs. Tight gas reservoirs have one thing in common--a vertical well drilled and completed in the tight gas reservoir must be successfully stimulated to produce at commercial gas flow rates and produce commercial gas volumes. Normally, a large hydraulic fracture treatment is required to produce gas economically. In some naturally fractured tight gas reservoirs, horizontal wells and/or multilateral wells can be ...
Abstract Starting in the early 2000's, we began to see increasing use of Hydrajetting for perforating as a companion to multi-stage fracturing operations. Bundling it within this larger service operation provides for an opportunity to overcome the added costs of using coiled tubing (CT) by developing methods that would allow the CT to stay in the wellbore while performing perforating only minutes prior to fracturing through the new perfs. This can be accomplished by using several different methods for isolating the zone just stimulated without tripping the CT string. This is most cost-effective where the well does not still have a rig, and even more beneficial if the other competitive options for stimulation would also require a stand-by CT string (for screenout, or in case of premature plug setting). More recently, the development of newer types of jetting tools has proven to bean effective method to revive higher perm zones that have recovered very little of the Oil in Place (OIP), especially where well architecture such as slotted liners and bare open hole completions have few or no competitive stimulation options. Several interactions of improving tool life have been accomplished during the past decade, and the need for less horsepower for effective multi-stage fracturing operations allows much smaller footprints than for the commonly applied North American style multi-stage fracturing operations. Also, in countries where any type of explosive charge is very highly guarded and regulated, CT Hydrajet perforating has seen significant application as a stand-alone well completion component. This paper will briefly review the tool advancements and highlight the various applications where Hydrajetted perforations empower various initial completion stimulation methods/techniques as well as several different re-frac recompletion successes from moderate permeability formations to nanodarcy sands and resource reservoirs. Also, some general comparisons of costs vs. the more commonly used perforating/stimulation/completion approaches will be provided, as well as discussion of well production comparisons where available. Introduction This paper will first provide a historical background for perspective on conventional shape charge perforating, then review/compare the benefits and limitations of CT deployed application for abrasive jet perforating. Next, the discussion will center on the revolutionary process introduced in the late 1990's (Surjaatmadja 1998; Eberhard et al. 2000) which began the modern expansion of Hydrajet perforating technology and application. This process started experiencing increased applications into the early 2000's and can be classified as Hydrajet-Assisted Fracturing (HJAF), where all the proppant slurry is pumped through jet nozzles immediately following the Hydrajet perforating stage with no interruption to pumping and repeated multiple times to provide multi-stage fracturing as it is pulled step-wise through a horizontal well. It was introduced before horizontal wells were common, and is still in use today. The third section will cover the process of multistage continuous applications of Hydrajet perforating through CT and then pumping the fracturing slurry down the annulus of the CT and the casing with an immediate isolation of the fractured interval and thereafter repeating this process many times as the CT moves up the hole. This achieves significant time savings as only one CT deployment will perf/stimulate/isolate multiple intervals in either vertical or horizontal completions. Several variations of this process are discussed that, in general, perforate using CT, then fracturing operations are pumped down the annulus, then the process is repeated up hole several times. Various methods to isolate the current fracturing zone from those downhole are employed without removing the CT from the wellbore. In the final section, the application as a CT deployed stand-alone perforating service process, including case histories in conventional completions and unconventional formation well completions, is presented.
Rodrigues, Valdo Ferreira (Petroleos Brasileiro S.A.) | Neumann, Luis Fernando (Petrobras S.A.) | Torres, Daniel Santos (Halliburton Energy Services Group) | Guimaraes De Carvalho, Cesar Roberto (Schlumberger) | Torres, Ricardo Sadovski (BJ Services Do Brasil Ltda.)
Abstract This paper presents a brief review of the available techniques in the oil and gas industry to complete and stimulate horizontal wells, with emphasis on low permeability carbonates. These techniques can also be applied in non-conventional reservoirs, particularly in tight formations. The paper starts by reviewing the lessons learned in some chalk fields in the North Sea (Dan, Halfdan, South Arne, Valhall and Eldfisk) and in a few pilot projects offshore Brazil (Congro and Enchova). Based on these lessons learned and in the broad literature, the paper devises some considerations on the methodology to select completion and stimulation techniques for horizontal wells. Cased and cemented horizontal wells, in addition to open hole and perforated/slotted liners wells are addressed. The macro aspects of field/area management are stressed as the completion and stimulation drivers. The key parameters for designing, implementing and evaluating horizontal completion and stimulation are presented, emphasizing the most common failures and the controversial aspects. The paper presents a summary of mature field and new scenarios that are candidate to horizontal completion and stimulation in Brazil and other Latin America countries. Then it makes a few comments on the resources available in Latin America to face the mentioned opportunities and related challenges. It is supposed that this brief review will be useful for the low permeability scenarios in Latin America and worldwide. Introduction This paper presents a brief review of the available techniques in the industry to complete and stimulate horizontal wells, with emphasis on low permeability carbonates. The emphasis on low permeability carbonates in this work is justified by the renewed importance of this scenario in Brazil and other Latin America countries. Although it does not focus on nonconventional reservoirs, such as tight gas, it is related to them as stimulated horizontal completions have been used on their development. This paper focuses fracturing stimulations, also making a few references to matrix stimulation. It also assumes that a horizontal well has already been justified and what is being discussed is its completion and stimulation. The paper starts by reviewing the lessons learned in some chalk fields in the North Sea (Dan, Halfdan, South Arne, Valhall and Eldfisk) and in a few pilot projects offshore Brazil (Congro and Enchova). Then it devises some thought on the methodology used to select completion and stimulation techniques for horizontal wells. It address cased and cemented horizontal wells, in addition to open hole and perforated/slotted liners completions. The key parameters for designing, applying and evaluating horizontal completion and stimulation are presented, underlining the most common failures and the controversial aspects. Completion and Stimulation of North Sea Low-Permeability Carbonates The North Sea low permeability chalks are taken here as a reference due to the outstanding technological evolution verified there in the last decades. Amongst more than ten fields producing from these reservoirs in the North Sea this paper focuses on the Dan, Halfdan, South Arne, Valhall and Eldfisk fields. The main characteristics of these fields are: shallow waters (43 to 69 m), dry completion, high volumes of OOIP (1.6 to 2.9 billions barrel), low permeability carbonates (0.2 md to 10 md) with microfractures in the central areas (10 md to 120 md), high porosities (up to 48%), soft to very soft chalks, small to medium net pays (15 m to 65 m), high oil saturation (up to 97%), and light oils (about 36o API). What most distinguishes these fields is their over-pressured soft chalks which are subjected to a high degree of compaction under pore pressure depletion, resulting in loss of drilling fluids, rapid production decline, well failures and seafloor subsidence. On the other hand the positive effects of rock compaction as a reservoir drive energy, outweigh by far the negative ones. The recovery factor under primary recovery can be as high as 30%. In general the North Sea chalks experienced an evolution from vertical/directional wells stimulated with acid treatments to multiple fractured horizontal wells.
Tight gas is the term commonly used to refer to low permeability reservoirs that produce mainly dry natural gas. Many of the low permeability reservoirs that have been developed in the past are sandstone, but significant quantities of gas are also produced from low permeability carbonates, shales, and coal seams. Production of gas from coal seams is covered in a separate chapter in this handbook. In this chapter, production of gas from tight sandstones is the predominant theme. However, much of the same technology applies to tight carbonate and to gas shale reservoirs. Tight gas reservoirs have one thing in common--a vertical well drilled and completed in the tight gas reservoir must be successfully stimulated to produce at commercial gas flow rates and produce commercial gas volumes. Normally, a large hydraulic fracture treatment is required to produce gas economically. In some naturally fractured tight gas reservoirs, horizontal wells and/or multilateral wells can be used to provide the stimulation required for commerciality.
Abstract Growing energy demand is leading the industry to re-evaluate resources found in challenging conditions such as unconventional formations. Cost-effective development of these resources depends upon strategic application of advancing production solution technologies. To enhance production and improve recovery processes, more efficient perforating and fracturing methods have evolved along with advancements in wellbore production hardware via use of solid expandable tubulars or combinations of solid expandable and conventional tubulars. Expandable technology applied as a completion/production string provides an optimized or customized wellbore that can facilitate increased fracturing rates, resulting in improved conductivity and enhanced hydrocarbon production. A fully expandable or combination system with standard casing can provide an integral component in either new wells or re-entry wells where low-permeability reservoirs, such as those characteristic of unconventional formations, require isolation and separation for pinpoint hydraulic fracturing. Although successful stimulation is routinely attained from hydraulic fracturing, ancillary downhole tools, such as conventional completion equipment, often compromise results by restricting flow and affecting pressure performance. Solid expandable swellable systems can optimize the fracturing parameters by maintaining larger diameters and providing positive seals for selective multi-zone isolation purposes. These production systems consist of expanded sealing sections in combination with expandable or conventional intermediate tubulars utilizing premium connections thereby providing a superior completion solution for mechanical diversion. Right-sizing the wellbore to the reservoir can provide operators significant cost savings, even more so during these economic times. Utilizing larger diameter expandables in the horizontal wellbore allows operators to first optimize the fracture program to the potential of the reservoir then develop the well program to accommodate the fracturing rates and volumes as well as the surface pumping facilities. This can result in slimmer surface and intermediate sections at much lower cost without compromising the overall stimulation completion program nor planned production and recovery. This paper will discuss the integration of expandable systems with other technologies and cite case histories to illustrate the effectiveness of solid expandable systems in enhanced production and fracturing applications. Introduction A large percentage of the world's future energy demands will be fulfilled by unconventional natural gases that include tight gas, coalbed methane (CBM), shale gas, deep earth gas, geo-pressured gas, and methane hydrates. Unconventional gas reservoirs require the formation to be fractured by hydraulic means to improve the formation productivity by providing a conductive path and joining the existing fractures and cleats in the reservoir (Zahid 2007). Ultimate recoverable unconventional gas resources in the U.S. are estimated to be about 750 Tcf of which 170 Tcf are in coalbeds, 480 Tcf are in tight gas sand and 100 Tcf are in shale (Stark 2007). The major unconventional gas reservoir types include tight reservoirs, CBM, shale's and hydrates. To some degree, there has always been production from unconventional reservoirs in virtually all North American basins in the United States such as Rocky Mountains, South and East Texas, north Louisiana, Mid continent, Appalachia, Jonah/Pinedale, Natural Buttes, Wilcox Lobo, Cotton Valley/Travis Peak, and Clinton/Medina. (Arukhe 2009) Estimates of shale gas in the US range from 500 to 1,000 Tcf, while the Gas Technology Institute calculates ~780 Tcf. The US Energy Information Administration estimates that US shale's contain 55.42 Tcf in recoverable gas. Shale plays with potential occur across the United States from southern California through the Rocky Mountains, across the Midwest into the Michigan, Illinois, and Appalachian basins in the east and as far south as the Black Warrior Basin in Alabama. (Lyle 2007)