Wells in the Montney Formation area, British Columbia, Canada, were designed as monobores and include surface and long lateral production casings. The decision to modify the openhole (OH) completion to a cemented sleeve system presented some concerns. A comprehensive data set from all prior cement operations was compiled and analyzed. This data showed severe gas migration to surface for both an OH completion and cemented lateral well. Computational fluid dynamics (CFD) and a finite-element simulator were used to evaluate both conventional and foam cement options using actual centralization and caliper log data. The results from this analysis identified a gas-flow potential factor (GFP) was of an order of magnitude where only compressible, foam cement would provide the required properties to achieve competent, long term zonal isolation. The characteristics of foam cement include a high kinetic energy that assists removing immobile mud trapped on the low side of the casing. Additionally, in this case, using a foamed spacer further improved mud removal from the annulus, resulting in improved displacement efficiency, as observed in the final cement evaluation logs. Filtrate loss and reduced hydrate volume can allow gas migration, giving rise to surface casing vent flow (SCVF) while the cement is curing. Foamed cement helps create a highly compressible cement system that can compensate for these volume decreases and reduce the potential for SCVF. The ductile properties of the set foam cement help mitigate the likelihood of cement debonding and cracks forming during hydraulic fracturing operations, which also helps to reduce the potential for SCVF.
Lost circulation is a major contributor to nonproductive time (NPT). It occurs during drilling as well as while cementing the well. To cure the losses, lost circulation materials (LCMs) are widely used. In severe cases when the fracture size is larger than the LCMs, sealing is not effective and does not sustain high differential pressures. The focus of this study is to provide a solution to plug wide natural fractures at high differential pressures using LCM in cement. Evaluation of LCMs was based on performance tests conducted using a permeability plugging apparatus (PPA). The individual LCMs and combinations of them were used to perform the study. High differential pressures of 2,500 psi and slot widths of 1, 3, and 5 mm were used during testing. Observations were made in terms of time to form the seal, cumulative volume of cement slurry lost before a seal was formed, and the efficiency of the seal. The cement slurry loaded with LCM was tested for rheology, suspension, and compressive strength development. LCMs having different geometry, such as granular, lamellar, fibers, and resilient graphite, were studied either individually or in combination. For a 5-mm slot and differential pressure of 2,500 psi, it was observed that the combination of LCMs performed superiorly compared to the individual LCMs in terms of loading required, time to plug, and slurry lost before an effective seal was formed. Fibers are bridging material that form an interlocking net over the pores or fracture and prevent other particles and fluids from passing through. This physical interaction of LCMs with the cement slurry forms an effective seal that demonstrates resiliency at high differential pressures and wide fracture widths. Inclusion of these LCMs has minimal effect on other slurry properties, such as compressive strength and stability. This paper also presents observations for various potential fracture widths vs. LCM combinations based on these results. A combination of LCMs was developed that can be used in extreme loss circulation zones to seal wide fractures at high differential pressures.
Hollow-glass microspheres (beads) are widely used during oilwell cementing operations to produce lightweight cement slurries; this paper discusses a new method of blending hollow-glass beads into cement slurries by creating a storable liquid suspension of hollow-glass microspheres (liquid beads). This new method enables efficient delivery of lightweight cement slurries in offshore and remote locations by eliminating bulk-blending logistics. The concept of liquid beads is not new; however, earlier attempts to develop liquid beads or similar products generally failed to address the storability problem. The buoyancy force tends to lift the beads to the surface of the suspension, forming a gel or crust and causing the mixture to lose flowability within a relatively short period of time. A special chemical-additive package developed in this study significantly extends the storability of liquid beads. This paper compares the gelation time of different liquid-bead formulas and evaluates the performance of cement slurries prepared with liquid beads. Laboratory test data show that the chemical-additive package developed in this study can extend the storage time (shelf life) of liquid beads from a few hours to at least one month without reagitation at room temperature; the shelf life can be further extended to at least one year with regular reagitation of the mixture. Cement slurries prepared with dry-blended beads and those prepared with liquid beads exhibit similar performance in terms of laboratory test results, such as free fluid, fluid loss, thickening time, and hydration kinetics. The liquid-bead system developed can be produced with cement batch mixers for field use and remain stable in tote tanks for at least several months with regular recirculation. Liquid beads can be added to cement slurries through liquid-additive pumps during a cementing operation. A novel liquid-bead product that can be stored for extended periods of time without separation is presented here along with necessary laboratory testing, actual field applications, and field-application case histories using liquid beads to produce low-density cement slurries.
Cement slurries have been designed to remain liquid for extended periods of time (> weeks) until exposed to a radiation source to provide a triggered activation mechanism. The cement setting occurs in two stages. First, a triggered setting of an aqueous phase system forms a stiff gel; then, the gel hardens further and develops strength because of cement hydration. The initial set can be accomplished by means of the triggered mechanism, while final engineering properties are provided by the hardened cement. This paper describes the design and results of this initial work detailing the rheological behavior and mechanical properties of cement slurries on exposure to 14 MeV neutron radiation from an accelerator and ionizing sources currently used in wellbore logging, such as gamma radiation. Additionally, other radiation sources are described in terms of their potential for use in a wellbore environment. The triggered response of this system with relation to neutron energy and admixtures used in the cement design to impart direct response is discussed. Particular details are presented relative to usage of commercially available radiation sources and their efficacy in a wellbore environment. Correlations between energy output, calculated energy absorption, and cement response summarize the effects of this ionizing radiation on cement slurries containing admixtures designed to respond to such exposure. The discussed cement systems employ monomer and polymer chemistry specifically selected for use with radiation triggered systems. Use of these chemistries in cement as additives and in other systems, such as spacer fluids or drilling fluids, is demonstrated.
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