No abstract

A rotating tension anchor was developed to improve the cement bond by enabling rotation of the production casing of steam injection wells during cementing. This would be a world-first application of this casing pre-tensioning system in the application of steam well design. A good cement bond is crucial for the integrity of a well; this is especially true in the harsh environment created by a 300°C injection temperature in steam well applications. A common and relatively simple approach to improve the cement bond quality is to rotate the casing during cementing. The rotation creates a helical flow pattern, which has an improved displacement efficiency compared to a uniaxial flow. The design of steam injection wells in this heavy oil field requires a deep-set anchor to pre-tension the casing string with the required pick-up force. The existing anchor system had to be engineered and modified to enable casing rotation during cementing. Although no breach of integrity has been found in previous steam injection wells, the operator identified improvement potential for the long term cement integrity through ultra-sonic cement bond measurements of existing wells. The 7-in production casing of a steam injection well was pre-tensioned with 264.000 lbs [120 metric tons] overpull and rotated with 20 revolutions per minute during cementing. This world-first field trial of a rotating anchor tensioning system demonstrates, that the existing tension anchor system can be modified to enable rotation of the casing. An ultra sonic cement bond run, several weeks after cementing, confirmed that use of this equipment produced an improved cement bond quality compared to offset wells of similar age and status.

A novel well concept to unlock reserves from mature gas fields in Northern Germany has been developed. This concept combines cemented completions with through-tubing coiled-tubing drilling to enable significant cost reductions using ultra slim hole drilling in sour gas bearing, Upper Permian Zechstein dolomite reservoirs. Once gas reservoirs mature, drilling of conventional infill wells can quickly become economically unattractive. Often this leaves resources untouched and it limits the economic life span of a field. To improve the economics of infill drilling in deep and mature gas fields significant cost reductions are necessary. These cost reductions can be achieved by changing the proven, yet costly, casing scheme to an ultra slim hole well concept. Besides unfavorable economics another challenge while drilling with conventional technology in mature fields can be the reduced inflow performance caused by formation damage. This challenge can be overcome by under- or at-balanced drilling, which is enabled by through-tubing coiled-tubing drilling. Despite improved efficiencies gained from knowledge by drilling many offset wells, the estimated gas volumes are not sufficient to justify drilling of new wells with the established and conventional well design. Therefore, the operator prepared an advanced ultra slim hole well concept. The casing shoe setting depths remained unchanged, however the hole sizes are reduced significantly. The openhole reservoir section is changed from 5.875-in to 2.5-in and this section is drilled with coiled-tubing and through the installed completion. The size of the completion is selected to be 3.5-in and it is cemented in a 4.125-in hole. In this application, the cemented 3.5-in completion eliminates an entire 7-in liner that would be necessary in the conventional casing scheme. The remainder of the ultra slim hole well is drilled with a 5-in drilling liner, a 7-in intermediate casing and a 9.625-in surface casing. This needs to be compared with the conventional casing scheme comprising of an 18.625-in surface casing, a 13.375-in intermediate casing, a 9.625-in production casing and a 7-in liner. The reduction in cost is estimated to be in the order of 40%. The presented concept can enable significant cost reductions and by applying this ultra slim hole concept further infill drilling in mature gas fields can become more economically attractive. Moreover, formation damage can be overcome by underbalanced drilling, which is enabled by drilling through-tubing with coiled-tubing. The synergies created by combining cemented completions with coiled-tubing drilling are presented in this paper.

Through-tubing (TT) drilling was used to drill Upper Permian Zechstein carbonates in Germany. The project was partially set up as an experimental performance comparison between a positive displacement motor (PDM) and a turbodrill bottomhole assembly (BHA) equipped with real-time logging tools. This would be a world-first drilling run for this size of turbodrill as well as the first turbodrill run on coiled tubing (CT) using this real-time data feedback. Through-tubing coiled tubing (TT-CT) drilling incurs significantly lower cost per drilled footage than conventional rotary drilling methods. A dedicated candidate selection process emphasized the geometry and extent of the pay zone, borehole stability, tubing geometry, and well integrity, which are all crucial for the application of TT-CT drilling. As a result of this screening process, well Sh Z1a, a horizontal sour gas production well was selected. Dedicated BHA designs were used for both the PDM and the turbodrill to allow for a direct performance comparison whilst drilling the section. TT-CT drilling was used to deepen the well. Initially, 410 ft [125 m] were drilled with a 2.283-in. [58.0-mm] impregnated bit and a 2.125-in. [54.0-mm] PDM using 1.750-in. [44.5-mm] CT suitable for sour service. An additional 148 ft [45 m] were drilled with a 2.283-in. [58.0-mm] impregnated diamond bit with polycrystalline diamond compact (PDC) cone cutters. This bit was run with a 2.125-in. [54.0-mm] turbodrill BHA equipped with real-time logging tools using a sour-service-suitable 1.750-in. [44.5-mm] CT with a fiber-optic cable. The section was drilled under total losses and through multiple natural fractures. While drilling with the real-time logging tool, internal and external downhole pressures, torque, and tension and compression forces were recorded to assist in the drilling process. Direct comparison of the PDM and the turbodrill BHA was made for rate of penetration (ROP), weights and pressures. The turbodrill BHA produced more than double the ROP than was possible with the conventional PDM BHA using less weight on bit and showed overall smoother drilling mechanics. The well is currently on production. The project showed that TT-CT drilling is a viable technology for production enhancement in depleted gas reservoirs and that new turbodrill technology generates significant performance improvements over conventional drilling tools.