Search

The advent of mega-sized hydraulic fracturing jobs which incorporate increased proppant per foot density, enlarged fluid volumes, tighter cluster spacing, and shorter stages in the Bakken/Three Forks play, have led to significantly higher IP's on the order of 20% over the past two years. Yet despite this dramatic increase, concerns exist as to whether treatments are fully optimized with respect to costs of overall volumes, rates, and concentrations. This paper describes two case histories, one in the Middle Bakken and one in the Three Forks formations of the Williston Basin, where a multidisciplinary geoscience and engineering team was assembled to attempt to answer the optimization question within the confines of real-world operational logistics and cost constraints. In these case histories, an optimization process is described that begins with wellbore context. The consideration of offset wells in the area, data analytics processes considering reservoir quality, and perceived successful completions for the area are incorporated as input. Detailed layered and geomechanical models are then constructed using drilling, neural network and public domain data to produce optimized perforation cluster design and grouping in precise fracturing stages. A rigorous planar 3D hydraulic fracturing model is used to simulate fracture geometry characteristics including height growth, half length, and aperture. Lastly, proppant tracing and production modeling were used to validate the approach used. The result of the project was to develop an optimization process incorporating the multidisciplinary technical team's expertise to provide an integrated, cost-effective completion design that would lead to more rigorous support for why these engineering decisions were taken. In addition, a secondary goal was to leverage software and database capacity for completion decisions into a "best practices process" that would neither burden the existing E&P staff nor hinder the completion timing. The resultant case study captures the process, technology analysis, weighted benefits, takeaway learnings, and results from two such wells within the Williston Basin.

This paper describes the successful combination of different stimulation techniques during the development phase of an offshore field in Congo. A total of four wells were drilled and completed during 2008-10. The target reservoir, the Sendji carbonates, has a total thickness of 150-170 vertical meters with an interlayer of ten meters. It is composed of silty-shaly dolomitic and quarzitic sandstone with interbeds of shale and sand grading to sandstone and silt with dolomitic cement characterized by very poor petrophysical properties. Laboratory testing with cuttings showed that formation is more than eighty percent soluble with fifteen percent hydrochloric acid. The typical well has an average azimuth and inclination of 60 and 350 degrees respectively, in the target reservoir. A good quality cementation job of the casing was required in order to ensure isolation from the aquifer. The well completions are both open and cased hole multistage fracturing completion systems. Selected zones of varying lengths were hydraulically fractured by using proppant / seawater-based borate crosslinker fluid or by using twenty percent delayed, viscoelastic and straight acid. Two wells were stimulated by means of proppant fracturing while the other two by acid fracturing. Due to upper / lower water zones with no bounding beds, it was important to define formation mechanical properties for fracturing designs in order to avoid fracturing into water bearing layers. A Mechanical Earth Model (MEM) was created by using sonic anisotropy measurements, modular dynamic test results, and other common electrical logging data together with drilling parameters. The detailed study of design methodology, different stimulation fluids and operation sequences are described. Particular attention will be given to the comparison of well responses to multi-stage proppant and acid fracturing techniques.