Seven Generations Energy Ltd. (7Gen) has drilled several horizontal wells in the extremely liquids rich Montney formation in the Karr Kakwa area of central western Alberta. Over the last two years we have seen progressively shorter drilling times as well as a marked increase in production as a function of optimal hydraulic fracturing recipes and completion installations. This paper will discuss the systematic approach taken by well construction engineers to optimize drilling performance through bit selection coupled with vibration mitigation and hydraulics optimization. Further technologies that will be discussed and will/have been be implemented are torque mitigation technologies to mitigate stick slip and the use of managed pressure drilling techniques to decrease mud density and further increase ROP’s. This paper will also discuss the coincident work done to optimize fracture treatments as a function of rock strength and measured gas response while drilling.
The underbalanced drilling of horizontal wells involves the injection of gas either with the drilling mud or via a separate string to that through which the drilling mud is injected. Nitrogen is generally used to prevent fire and explosion hazards during drilling; however, this adds considerably to the cost. Costs can be reduced by the replacement of nitrogen injection with normal air, de-oxygenated air or vitiated air (air/nitrogen mixture), but this increases the potential for flammable, or explosive, mixtures to be present in the wellbore and surface piping during underbalanced drilling. Safe operational ranges of oxygen-containing drilling mud mixtures can be determined if the flammability of the mixtures is known. Several studies were carried out to determine the flammability of these mixtures as a function of pressure to minimize the potential for downhole and surface explosion, and to set out the guidelines for safe underbalanced drilling operations of horizontal wells. A specially-designed apparatus was calibrated utilizing methane/air mixtures, then the ignition and the flammability characteristics of various mixtures of air, drilling mud and live oil were established over a range of pressures from atmospheric to 2,100 kPa at 21 ° C. Additional tests were carried out utilizing drilling mud, live oil, and either a nitrogen/air mixture (vitiated air) or de-oxygenated air. Flammability limits were determined for each series of experiments, and the results used to design the safety features for the underbalanced drilling of several horizontal wells. The field trials proved successful, and significant cost savings were realized. Introduction A growing demand for maximizing heavy oil production in a cost-effective manner has led to the development of a variety of novel technologies. One such technology involves the drilling of wells employing underbalanced or near-balanced drilling procedures in order to minimize the possibility of formation damage due to drilling fluid invasion. There is a potential for flammable, or explosive, mixtures to be present in the wellbore and surface piping during this type of drilling operation. In underbalanced drilling, normal air or an oxygen-containing gas (usually vitiated air, which is air mixed with nitrogen, or de-oxygenated air, which is air with some of the oxygen removed) is injected and/or circulated with the drilling mud to reduce the potential for formation damage due to whole mud, fluid filtrate and solids invasion into the hydrocarbon-bearing formation. The study presented in this paper was performed to determine the safe conditions for underbalanced drilling of Husky Wainwright Well 15B-31-44-4 W4 using compressed air and liquid nitrogen. This well, located in the Camrose reservoir, which is a fractured vugular carbonate at 690 m TVD, was proposed to be drilled 550 m laterally(1). The main objectives of this investigation were:To establish the flammability of mixtures of air, live heavy oil and drilling mud as a function of pressure, andTo determine the optimum composition of vitiated air (nitrogen- air mixture), based on the flammability data, in order to minimize the potential for ignition or explosion during the underbalanced drilling operation.
The application of managed pressure drilling (MPD) is becoming more widely spread throughout the world. It is well known that MPD has less hydrostatic head during drilling therefore the rate of penetration (ROP) is increased. This is due to the reduced rock confinement and chip hold down effects. By simulating the conventional drilling and MPD of a well in advance the benefits of MPD can be quantified in terms of increase in ROP and therefore the economical benefits. Applying a commercially available drilling simulator (1)meter by meter drilling performance is analyzed, first simulating and optimizing a conventional drilling operation and then performing the same procedure for a MPD operation in Western Canada. The additional costs of the MPD operation are integrated into the economical analysis. The analysis shows that the ROP during MPD in the higher mud weight regime of the well is improved from 60 to 80 percent. In addition to the faster drilling during MPD the drill bits last longer due to the lesser hardness of the rock being less confined and therefore also reducing the amount of bit wear and the number of bits required and tripping time. Overall the results indicate that the MPD operation reduce the drilling cost of gas wells in Central Alberta more then 20 percent and due to the reduced time at the location less environmental impact is seen. Introduction The first objective of this exercise was to develop a "base case" drilling simulation from which subsequent optimization simulations could be run. An apparent rock strength log (ARSL) was developed based on actual drilling data and formed the backbone of all subsequent calculations. The second objective of the exercise was to compare the non-optimized base case (as above) with an optimized base case. Based on previous experience, drilling economics should improve by approximately 25%. The third and primary objective of this exercise was to compare the optimized base case with an optimized Managed Pressure drilling (MPD) case and, if possible, to justify the additional cost of implementing MPD technology.
The advantages of foam drilling over conventional mud drilling have long been recognized and include faster penetration rates, longer bit life, prevention of lost circulation and less formation damage to the producing reservoir resulting in overall drilling cost reduction and higher production rates. Careful practical design and control of gas and liquid volumes, injection pressure and annular backpressure must be applied in foam drilling to achieve the optimum results. Optimization of foam drilling is done by drilling with the lowest acceptable bottom hole pressure and making sure that the wellbore is kept clean. This is done by applying an integrated flow model that accounts for both the compressibility of the foam, the hydrostatic column and the frictional pressure losses in conjunction with minimum hole cleaning requirements. The model is integrated with the hole cleaning requirements to obtain the balanced and lowest bottom hole pressure for the operation. The equations, procedure and sample application of this method are presented herein. Using this UBD approach on Iranian oil fields indicates large cost savings. The drilling operations in the Shanoul and Parsi fields shows as much as 60–70 percent reduction in bottom drilling time using foam drilling compared to conventional mud drilling. Using the optimum volumetric model for foam drilling and a series of simplified hole cleaning charts presented herein, the foam drilling program for the Shanoul field enabled determination of optimum drilling and hole cleaning parameters in this field. This paper presents results from programming of near balanced conditions using a new foam drilling program designed for the Shanoul field. The target formations were hard, fractured and depleted limestone formations with low pressure. The paper also compares the results to similar wells drilled with aerated fluids and conventional muds, which indicates the foam drilling as being superior in terms of rate of penetration longer bit life and less wellbore instability. A drilling cost study comparing conventional, aerated and foam drilling is also presented. Introduction Parsi field is located approximately 100 Km South East of Ahwaz and Shanoul field location is at south of Fars provience. Parsi field is one of the largest Iranian oil and gas fields. So far 68 wells have been completed in Asmari formation of this field. The initial reservoir pressure of Parsi Asmari was approximately 3800 psi. By December 2001, about 1.48 Billion STB had been produced, with a pressure decline of about 800 psia. Shanoul field is still producing oil and gas with a high formation pressure condition (over 3500 psi) and it seems that the average reservoir pressure has been declining during four years of production with no pressure maintanance. Stable and Stiff Foam Drilling is the best UBD technique that can be proposed for drilling these field formations for the following reasons:Stable foam possesses a solids carrying capability much higher than that of liquids.Drilling with foam gives faster ROP.Foam velocity and pressure consideration help us to control washing effects and also formation water influx.
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