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The Pelican Lake heavy oil field located in northern Alberta (Canada) has had a remarkable history since its discovery in the early 1970s. Initial production using vertical wells was poor because of the thin (less than 5m) reservoir formation and high oil viscosity (600 to over 40,000cp). The field began to reach its full potential with the introduction of horizontal drilling and was one of the first fields worldwide to be developed with horizontal wells. Still, with primary recovery less than 10% and several billion barrels of oil in place, the prize for EOR is large. Initially, polymer flooding had not been considered as a viable EOR technology for Pelican Lake due to the high viscosity of the oil, until the idea came of combining it with horizontal wells. A first – unsuccessful – pilot was implemented in 1997 but the lessons drawn from that failure were learnt and a second pilot met with success in 2006. The response to polymer injection in this pilot was excellent, oil rate climbing from 43bopd to over 700bopd and remaining high for over 6 years now; the water-cut has generally remained below 60%. This paper presents the history of the field then focuses on the polymer flooding aspects. It describes the preparation and results of the two polymer flood pilots as well as the extension of the flood to the rest of the field (currently in progress). Polymer flooding has generally been applied in light or medium gravity oil and even today, standard industry screening criteria limit its use to viscosities up to 150cp only. Pelican Lake is the first successful application of polymer flooding in much higher viscosity oil (1,000-2,500cp) and as such, it opens a new avenue for the development of heavy oil resources that are not accessible to thermal methods.
The Pelican Lake heavy oil field located in northern Alberta (Canada) has had a remarkable history since its discovery in the early 1970s. Initial production using vertical wells was poor because of the thin (less than 5m) reservoir formation and high oil viscosity (600 to over 40,000cp). The field began to reach its full potential with the introduction of horizontal drilling and was one of the first fields worldwide to be developed with horizontal wells. Still, with primary recovery less than 10% and several billion barrels of oil in place, the prize for EOR is large. Initially, polymer flooding had not been considered as a viable EOR technology for Pelican Lake due to the high viscosity of the oil, until the idea came of combining it with horizontal wells. A first – unsuccessful – pilot was implemented in 1997 but the lessons drawn from that failure were learnt and a second pilot met with success in 2006. The response to polymer injection in this pilot was excellent, oil rate climbing from 43bopd to over 700bopd and remaining high for over 6 years now; the water-cut has generally remained below 60%. This paper presents the history of the field then focuses on the polymer flooding aspects. It describes the preparation and results of the two polymer flood pilots as well as the extension of the flood to the rest of the field (currently in progress). Polymer flooding has generally been applied in light or medium gravity oil and even today, standard industry screening criteria limit its use to viscosities up to 150cp only. Pelican Lake is the first successful application of polymer flooding in much higher viscosity oil (1,000-2,500cp) and as such, it opens a new avenue for the development of heavy oil resources that are not accessible to thermal methods.
Horizontal wells have shown such gains in productivity in many applications that the damage associated with longtime exposure to drilling fluid was, in many cases, accepted. In addition, the difficulty of removing formation damage in a horizontal well has compounded the problem. With many horizontal wells now being left in an openhole status, formation damage becomes even more important. Coiled tubing (CT) drilling has grown from four jobs in 1991 to over 120 (estimated) jobs in 1994. The primary motivations for this growth have been:The ability of CT drilling to finish drilling a well in soft formations faster than a rotary rig, andSafe, rigless underbalanced drilling to greatly reduce formation damage in horizontal wells. This paper reviews the causes of formation damage, both from fluid/solids invasion and stimulation techniques to remove damage. An analytical model is used to estimate the productivity index (PI) for various horizontal and vertical permeabilities, well lengths, and reservoir thicknesses for comparison with results from several case studies. Options for underbalanced drilling including fluid selection, gas lift, and seal technology are discussed. Candidate selection criteria for those evaluating the possibility of underbalanced horizontal drilling are presented. INTRODUCTION Horizontal wells are particularly vulnerable to formation damage due to long drilling mud exposure time relative to vertical wells (easily 30 times) and reduced cleanup velocity (easily 1/5) with production spread over the long horizontal. In spite of this, horizontal wells are the most important success story in the oil business in the last 10 years. Average gains in productivity1,2,3,4 of two to seven times the vertical wells in reservoirs with matrix permeability have fueled the growth of horizontal drilling. In reservoirs with natural fracture, productivity indices of 20 to 30 times the vertical have been observed with ultimate recovery several times greater than for vertical wells.5 Ultimate recovery improvement with matrix permeability is not widely reported, although 1.5 to 2 times vertical ultimate recovery is expected in two Canadian reservoirs. Although the ultimate recovery may not be improved, the accelerated production often makes horizontal wells more economically attractive in spite of the higher cost of the average horizontal well which is 1.2 to 2 times the vertica.3
Underbalanced drilling is quickly becoming an important technology in the Canadian oil and gas sector. While drilling impairment has always been a concern, a significant increase in horizontal completions has brought this issue to the forefront. A number of stimulation techniques are available for overcoming impairment in vertical wells or shallow damage in horizontal wells, however, deeper matrix damage is often difficult to remove in long horizontal sections. With this in mind, Canadian producers have looked to underbalanced drilling to prevent damage caused by fluid leak-off and fines migration.Many of the oil and gas fields in Canada are subhydrostatic, therefore underbalanced drilling 'operations often require the entrainment of a gas 507 phase in the drilling fluid to generate the appropriate bottomhole pressures. In most cases, because of safety concerns, nitrogen gas is used.Two basic styles of nitrified underbalanced drilling are currently used with conventional rig drilling operations. One involves injecting nitrogen at the standpipe to co-mingle with the drilling fluid. The other, referred to as parasite injection, utilizes an external gas injection conduit that allows gasification of the drilling fluid in the vertical annulus. Either approach has specific advantages which must be considered for each application.An essential component of underbalanced drilling (UBD) success is effective two-phase flow modeling. Initial simulation is required to investigate and optimize various design options in the planning stage. An Overview of Underbalanced Drilling Applications in Canada SPE 30129This is often followed up by providing onsite support to assess actual job parameters and make any required design modifications.This paper focuses on these two UBD techniques, addressing the advantages and limitations of each. Two-phase flow analysis and job design will be discussed. A summary of the jobs completed, operational details and production results will be given.
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