During the past decade, the completion technique used in liquid-rich unconventional plays in North America has undergone a transformation. Today, the vast majority of completions in these areas are open-hole (OH) graduated ball-drop fracturing isolation systems. This preferred completion type for horizontal wells is driven by the efficiency gains in fracturing operations and the production gains when compared to previously used completion techniques. Thousands of open-hole fracturing systems are run each year, with a continuously growing stage count.
Graduated ball-drop type completions rely on a sliding sleeve activated by a ball dropped from surface. Each ball travels the length of the lateral well to its intended operational depth, at which it meets a mated seat and isolates the wellbore below. Once the ball is in position, the sliding sleeve opens via the hydraulic force on the ball and seat, allowing a fracturing stage to commence. This dual function of the ball—activation and sealing—is of extreme importance for the stimulation treatment process. If the ball fails, it will result in bypassed pay zones and unintentional refracturing of previously stimulated zones. Although sometimes surface pressures can be used to infer ball behavior, often the pressure signals observed at surface cannot guarantee successful ball performance.
This paper will present an extensive study of ball performance under pressure for the most common ball materials in the industry. Phenolic, composite and metal alloy materials were explored with the pros and cons for each investigated. In particular three main areas were analyzed: 1) molding, layering and extrusion of material versus inconsistencies in ball performance; 2) ball deformation at high pressure versus pressure required to bring the ball off seat; and 3) comparison of the performance of phenolic, composite and metal alloy materials for ball fabrication and their performance at high temperature.
The conclusions from this paper provide operators the necessary information to consider when making completion and ball material decisions in their field operations. In particular, the results of this testing may illuminate some previously unexplainable occurrences in graduated ball sliding-sleeve systems. This testing clarified that not all fracturing balls pumped in horizontal wells perform equivalently under wellbore fracture conditions.
The Eagle Ford shale is a hydrocarbon-producing formation of significant importance due to its capability for producing at high-liquid/gas ratios, more so than other traditional shale plays. Situated in south Texas, the total Eagle Ford liquids production in 2007 was less than 21,000 bbl total. In 2011, production averaged 65,500 BOPD in the play (EIA, 2011). Activity in the Eagle Ford continues to increase because the benefits from producing high liquid yields across much of the play, along with attractive commodity prices, have made the Eagle Ford a more attractive development over many other shale reservoirs.
The rapid development of the Eagle Ford shale was enabled by horizontal drilling. In 2007 none of the reported production was from horizontal wells. In 2011 alone over 2,800 drilling permits were issued, virtually all of them for horizontal wells (RigData, 2012). The Eagle Ford shale has low-clay content, high-carbonate content, and is in an extensional basin, making it conducive to somewhat complex hydraulic fracturing (Martin et al, 2011). The plug and perforating technique has become the preferred completion method in the play due to multiple entry points creating complex fractures at a minimal cost. This completion technique requires a mechanical means for conveying perforating guns, such as coiled tubing (CT), wireline tractor or stick pipe, for the first fracturing stage at the toe of the well.
To streamline their completion process, an Eagle Ford operator chose to use an initiator valve that is run at the toe of the well as part of the final completion design. This pressure activated valve is capable of initiating operations on the first fracturing stage without the need for CT or other mechanical means of conveyance of perforating guns. Simple and robust, the valve is activated by a pressure increase from the surface. The valve uses a rupture disc for precise activation and a helical port design that allows for hydraulic fracturing to be performed through the valve into the cement and the formation. With over a dozen wells completed in the Eagle Ford formation by the operator, the valve has provided logistical and economic benefits to the streamlined completion process.
This paper describes the initiator valve completion tool and its application in the Eagle Ford shale. A case history is presented to show the specific design and operation of the initiator valve, as well as its benefits over other completion practices that target the first stage in a closed lateral system. Detailed activation of the valve and fracturing data through the valve are also presented.
Technology Update - No abstract available.
The Bakken is one of the most active basins in the world in terms of number of rigs, with over 200 operating on the US side of the US-Canadian border. Production has rapidly increased from 100,000 BOPD in 2005 to 600,000 BOPD in 2012 in the state of North Dakota with the majority of production coming from the Bakken (Uptream Online, 2012). Greater horizontal drilling activity and a continuing increase in the number of hydraulic fracture stages per lateral have helped North Dakota grow its oil production six-fold in just seven years.
The Bakken is a fairly tight dolomitic siltstone requiring hydraulic fractures to produce economically. The stage count for hydraulic fracture treatments averaged nearly three stages in early 2007 and increased steadily over time to nearly 30 stages in late 2011. Some wells have even been completed with 40 or more stages. With the ever increasing stage count, the question remains: has the economic stage count limit been reached in the Bakken?
This paper analyzes the stage count versus the production impact of horizontal Bakken wells to determine if the economic stage count has been reached in the play. Wells are grouped and analyzed based on geographic considerations to help normalize for changes in geologic attributes such as natural fractures, reservoir quality, and net pay. Lateral length was also taken into account as varied lengths can impact stage spacing and interference issues.
Analyses were run with various oil and well service costs to determine how the economic stage count may change over time. If the economic limit was not reached under certain circumstances, this paper analyzes possible scenarios to determine when the economic stage count would be reached. This approach should provide insight into how other unconventional oil plays can evolve in the future.
Liu, Guang Hua (PetroChinaDagang Oilfield Company) | Cui, Hui Kai (PetroChinaDagang Oilfield Company) | Fould, Jeremie Cyril (Schlumberger) | Lee, J.S. (Schlumberger) | Wang, Hailong (Schlumberger) | Zhang, Xingguo (Schlumberger) | Aviles, Isaac (Schlumberger) | Baihly, Jason David (Schlumberger)
Drilling activity has been steadily ramping up in China to meet the countries energy demand and government production goals. This is moving some activity to previously unexploited ‘tight' formations requiring hydraulic fracturing to produce economically. These formations have historically been producing with stimulated vertical wells and some horizontal un-stimulated wells. Many of these tight reservoirs exist in the Bohai Basin of Eastern China.
In order to quickly ramp up production to meet the governments' goals, new drilling and completion techniques are being used including completing horizontal wells with multistage hydraulic fractures in some fields. In some low producing areas new methods of isolating and stimulating wells are being investigated by the operator. New stimulation isolation methods must be streamlined as much as possible in order to achieve the production goals quickly and economically.
One of the new completion systems that was developed for cemented wells requiring multistage stimulation us generically called the treat and produce (TAP) completion system. This high efficiency completion system has recently been used in China's Dagang field to stimulate a horizontal well.
The TAP system was run by the operator in the Dagang field, where cased and cemented vertical completions are common and require artificial lift to produce. Horizontal cemented completions have been recently introduced as a means to increase field wide production. Although plug and perforating methods are
applicable for these wells, the client turned to a more efficient solution. TAP systems permit continuous pumping operations to be performed while precisely placing multiple hydraulic fracture treatments along the horizontal section; immediate flowback is possible for further production and efficiency gains.
In order to efficiently complete the horizontal well, a treat and produce (TAP) system was used in order to complete the well. This completion system uses a series of sliding sleeve valves that are installed as part of the casing string. These valves are actuated by pressure and sliding sleeves with graduated ball seats.
This paper describes the TAP completion system and its application in the Dangang field in China. TAP completions enabled optimized fractures placement and propagation in cemented completions that resulted in efficiency and production gains for the client, proving the application for the field. By means of a case history, the specific design and operation of the TAP completions system are discussed.