The oil and gas industry has operated in Denver Julesburg (DJ) basin for many decades. Currently in the basin, increasing population density and wellbore complexity have resulted in a heightened visibility of long-term well integrity. Failure can lead to future liabilities, loss of public trust, and a revoked right to operate. Operators must demonstrate commitment to well integrity to continue operating in the basin, yet many still report sustained casing pressure (SCP) on a significant portion of wells. Because SCP corresponds to the open communication of fluids to surface, it is a direct metric of well integrity failure. Regulations require operators to report and remediate instances of SCP on all wells. On average, clients experience one well with SCP for every five drilled. As a primary well barrier element, the cement sheath is vital to well integrity improvement. Enhanced placement techniques of conventional cements failed to prevent SCP, confirming that failure is derived from post-placement dynamic conditions. The solution must account for pressure and temperature stresses, preventing and mitigating mechanical failures throughout the well life cycle. A flexible and self-healing cement design provides a twofold response that is ideal for wells in areas, such as the DJ basin, with SCP risk. Mechanical properties are optimized based on the results of a mathematical stress model. Although Portland-based cement systems can be optimized to sustain higher levels of dynamic stresses, it is impossible to avoid a mechanical failure entirely. Therefore, a self-healing function is a critical secondary feature. The self-healing mechanism is designed to activate upon contact with an invading hydrocarbon and can be formulated for any type of hydrocarbon, from high gravity oil to dry gas. Flexible and self-healing cement has been successfully designed and implemented on approximately 250 wells in the DJ basin with a reduction to 2% instances of SCP. Elimination of SCP provides confidence in long-term well integrity, which is essential to continued operation in the basin.

Multistage hydraulic fracturingturing treatments in unconventional wells have greatly increased the number and magnitude of stress cycles that must be withstood by primary cement jobs. The stress cycling of hydraulic fracturingturing on Portland Cement, with its intrinsic mechanical properties, may present a risk to long-term well integrity. By modifying the mechanical properties of the set-cement to make it more flexible, the risk of compromising well integrity during hydraulic fracturingturing treatments can be reduced. The mechanical properties of set-cement designs can be tested in a laboratory setting. This allows quantification of the compressive strength, tensile strength, Young's modulus, and Poisson's ratio of the set cement. Hydraulic fracturingturing design software can be used to quantify the pressure and temperature cycles to which the inner diameter of the primary casing string will be subjected. A mathematical model is used to predict the potential risk of mechanical failure of the set cement based on the mechanical properties and the pressure and temperature cycles of the expected treatment. The mathematical model identifies risk of failure in tension, compression, and de-bonding. By adding flexible materials to Portland Cement in a reduced water, tri-modal particle-size-distribution blend, the Young's modulus can be reduced while relatively high compressive and tensile strength is maintained. According to the mathematical model, a cement sheath with these properties is at a low risk of mechanical failure in any of the three failure modes up to a certain hydraulic fracturingturing pressure. Wireline logging tools use ultrasonic waves to measure acoustic impedance and flexural attenuation for cement evaluation. These readings are used to assess the integrity of the cement sheath in a 360° solid/liquid/gas map around the casing. These logging data can be used to determine the presence and extent of damage to the cement sheath during the hydraulic fracturingturing operation. A hydraulic fracturingturing treatment was applied to a well cemented with optimized flexible and trimodal properties. Cement evaluation logs were run before and after treatment for comparison. The post-fracturingturing log showed no damage to the annular cement sheath.

One of the primary challenges of cementing and achieving effective zonal isolation is removing nonaqueous drilling fluid from the wellbore. Microdebonding of the cement sheath is a significant risk to overall well integrity, potentially leading to sustained casing pressure and health, safety, and environment (HSE) hazards. Field applications of a new fiber technology, designed with an optimized surfactant and mutual solvent package, have provided improved cement evaluation logs. Such trials also reduced or eliminated sustained casing pressure. This novel application of fiber technology in weighted spacers ahead of cement placement has been tested and evaluated with success. Modified rheometer rotors were among several new techniques developed to identify the efficacy of these cement spacer packages. These tests provide greater insight into fiber, surfactant, and mutual solvent performance, and have been validated in the field with ultrasonic and acoustic cement evaluation log results. Detailed laboratory analysis suggests superior effectiveness of the fiber, surfactant, and mutual solvent design. These preliminary results established the confidence to pursue a field trial on a number of development wells in an unconventional liquids play. Cement evaluation logs confirmed that the new technique successfully reduced microdebonding. Additionally, sustained casing pressure was significantly reduced, indicating that the log response correlates to a tangible improvement in well integrity. The novel use of fiber technology considerably improves the surface cleaning effectiveness of cement spacer package. Additionally, new laboratory testing procedures enhance our understanding of surfactant package function. Successful laboratory results were validated by field applications that reduced the microannulus in sample wells and minimized sustained casing pressure.

Historically, horizontal wells in the Bakken/Three Forks formations in the Williston Basin have been completed using open hole completions to maximize wellbore access. As the play was developed, operators moved to multistage completions using open hole packers. Lately, operators have been seeing various advantages of cemented laterals, including the opportunity for additional stimulation stages and the potential improvement of production. This has given rise to a field wide move towards cemented laterals. One challenge associated with cemented laterals can be increased near wellbore friction pressure during stimulation. This increased near wellbore friction pressure is related to the tortuosity as the stimulation treatment travels around the wellbore from the perforation tunnel to the primary fracture plane.Due to the increased near wellbore pressures during hydraulic stimulation in cemented laterals, acid treatments are frequently performed before hydraulic stimulation. Portland cement does not exhibit significant solubility in acid. For this reason, calcium carbonate is sometimes added to the cement to increase the solubility in acid. This paper aims to quantify the acid solubility with respect to time of some typical horizontal cementing solutions, and to determine the optimal cementing solution for minimizing near wellbore friction in cemented laterals. In an idealized situation, the near wellbore pressure could be decreased to nearly zero if all of the cement in the perforated interval was acidized away, while still leaving good zonal isolation of the cement sheath along the wellbore where there are no perforations.Laboratory testing shows that conventional cement designs exhibit a very small weight reduction when soaked in acid, and that reduction requires a long period of time to be achieved. Acid-soluble cement designs which use small concentrations of calcium carbonate exhibit slightly increased weight reduction after soaking in acid, but still requires a long soaking time for the dissolution to occur. To achieve maximum solubility in acid, the calcium carbonate concentration needs to be increased dramatically.When adding large quantities of non-cement materials, like calcium carbonate, to a cement slurry, the slurry properties and set-cement properties can be compromised. To achieve the required slurry and set-cement properties while achieving maximum calcium carbonate concentration and therefore acid solubility, a multi-modal particle size distribution cement design was used. This particle size distribution design allowed high weight reduction of after a short soaking time in acid, while still achieving a cement design that met all of the industry accepted best practices for cementing laterals.

The adsorption of small molecules onto functionalized, high surface area microporous materials is important for the advancement of industrial and environmental processes ranging from catalysis and chemical separations, to CO2 sequestration and energy storage. Over the past several years we have focused our research efforts on understanding the molecular interactions of these small molecules with a variety of microporous materials using in-situ powder diffraction methods to correlate structure with chemical properties. Background will be given on the design of gas dosing apparatus for in-situ diffraction studies at synchrotron X-ray and neutron powder beamlines. The result is that accurate doses can be made per quantity of interest (moles of cations, per unit cell, per pore, etc.), or under high pressures (100 bar), and/or chemical reactions can be followed versus temperature/pressure. Several of our recent investigations of CO2/N2/CH4 sorption in cation-exchange zeolites including Zeolite A (5A) and CHA are presented. While many industrial processes use zeolites to carry out these functions, more emphasis has been placed on metal-organic frameworks (MOFs) on late since their properties can be tuned by varying the synthetic components. A number of studies on an isostructural series, M-MOF-74, have been considered investigating why certain functionalization leads to increased specificity for applications such as CO2, O2, CO, and hydrocarbon separations. The ultimate goal is to use the knowledge gained to improve the design of new MOF materials.