Hydraulic fracturing technology is widely used to facilitate and enhance the gas recovery process from conventional and tight gas resources. Tight gas or unconventional reservoirs, that include very low permeability sandstones, carbonates, or shales, cannot be economically produced without hydraulic fracturing. Recently, much progress has taken place in the overall hydraulic fracturing procedures and the field implementations of advanced stimulation technology have produced good results. The proper selection of well trajectory, gel concentration, polymer loading, proppant type/size and concentration, perforation methods, locations for packer and frac port placement in a multistage fracturing assembly, number of fracture stages to cover the net pay, etc., have all contributed to successful stimulation and improved gas recovery. Even though stimulating gas reservoirs has become a routine application and much experience has been gained in this area, not all treatments are straightforward without problems and challenges. Unless a stimulation treatment is carefully designed and implemented, the post-stimulation results in moderate to tight reservoirs may not be encouraging, and can easily fall below expectation. The most essential step to close the gap between expected results and actual well performance is to understand reservoir characteristics and its potential to produce at a sustained rate after a successful fracturing treatment. Overestimation of reservoir flow capacity and achieved fracture geometry will also over-predict well performance. This paper addresses the importance and impact of detailed reservoir characterization and superior stimulation processes on final well performance. Several field examples from Saudi Arabia’s gas reservoirs are presented in the paper showing the value of effective well planning, reservoir characterization, application of hydraulic fracturing, and proper cleanup. The paper also illustrates the impact of drilling trajectory and wellbore reservoir connectivity on the proper placement of desired hydraulic fracture treatments and sustained gas production.
Stimulation treatments in Saudi Arabian gas reservoirs were initiated in 1998. Since then, stimulation gradually became the preferred technology to improve gas production and sustainability. Different technologies have been applied over the years, and only the best of them survived the test of time. Advances in completion technologies enabled drilling horizontal wells and completing them with multistage stimulation completions in either openhole (OH) or cased hole wellbores. The new generation of stimulation software allowed comprehensive modeling of hydraulic fracturing in a 3D reservoir simulation software platform. Advances in logging technologies allowed better estimation of rock mechanical properties, a major input for the fracturing design software. Channel fracturing technology mitigated the risk of screenout in proppant fracturing and enabled placing fractures with nearly infinite conductivity that helped in faster cleanup of the well and improved production. The new dualcrosslinked fracturing fluid provided a reliable solution for high-pressure/ high-temperature (HPHT) reservoirs that can sustain very high shear degradation. Viscoelastic surfactant (VES) based fracturing fluid limited fracture height growth, thereby allowing hydraulic fracturing in pay zones with nearby water zones. Emulsified acid allowed live acid to penetrate deeper into the reservoir. Fiber laden viscoelastic self-diverting acid proved to be an efficient diverting technique for matrix acidizing and acid fracturing. This paper provides an overview of the different technologies that make stimulation treatments highly successful.
A gas bearing carbonate reservoir has been under development in Saudi Arabia to exploit the nonassociated gas to meet the robust increase in gas demand. Initial penetrations showed reservoir heterogeneity with several gas-water contacts (GWCs), variation in reservoir pressure, presence of faults/channels, and H 2 S content and condensate yield. All these factors made it hard to meet the target developmental plans with conventional reservoir exploitation techniques. Therefore, several delineation wells were initially drilled to assess reservoir boundaries and resulted in an upside potential increase in reserves. Gas producing wells were placed based on calibrated 3D seismic impedance and simulation runs. Several strategies have been used to drill these wells targeting the best reservoir development, such as dual lateral, geosteering, horizontal and extended reach wells. Other technologies like multistage horizontal fracturing and underbalanced coiled tubing drilling (UBCTD) were so effective to enhance the wells' productivity from poorly developed and tight reservoirs. One main obstacle was to drill wells in populated areas and finding a more reasonable surface location that provides the most cost-effective drilling operations. This paper will address all these challenges been faced during the initial field development and the technologies and methodologies been used to achieve full field development and meeting the target gas production. Several field cases will be discussed in detail covering geological interpretation, simulation runs, drilling/completion operations, stimulation, production performance, and reservoir management. These strategies were found so effective in developing this gas field, that they are currently being implemented in other fields that will be put on production during the incoming business plan cycle. These strategies helped to confirm field boundaries, identify multiple GWCs, avoid areas dominated with water encroachment, optimize reservoir depletion, and extend production plateau.
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