Lost Circulation Materials for Sealing Large Fractures

Significant lost through natural fracture networks has made geothermal drilling very slow and expensive. Considering the fact that 50% of the costs in geothermal project is related to drilling, it is essential to address this matter. While there have been various lost circulation materials (LCMs) available in the market for treating fractures during drilling oil and gas wells, there is still a demand for a technology to seal large fractures. Considering limitations on the size of the particles that can be circulated through the drilling equipment especially bottomhole assembly (BHA), simply enlarging conventional LCM particles becomes ineffective for sealing large vugs and fractures. In this study, we use shape memory polymers (SMPs) to prepare programmed LCMs with various temporary shapes, which can transform to their permanent shapes with much larger dimensions as compared to their temporary shapes. The basic idea is that, after recovery, the SMP-based LCMs form an entangled network across a large width of fracture, and SMP particles, recovered within the network, filling in the pores to form an effective sealing.

 

Nanoengineered cement for sealing leaky gas wells

Leaking natural gas wells are considered a potential source of methane emissions, and a new nanomaterial cement mixture could provide an effective, affordable solution for sealing these wells. We have invented a very flexible cement that is more resistant to cracking. That’s important because there are thousands of orphaned and abandoned wells around the world, and cracks in the casings can allow methane to escape into the environment. Adding almost 2D graphite created a cement mixture that better filled these narrow spaces and that was also stronger and more resilient. Our group has develop special method for surface treatment of these nanoparticles for their uniform and effective dispersion in the cement slurry.

 

Hydraulic Fracturing In Naturally Fractured Reservoirs

Hydraulic fracturing has been the most effective stimulating technique to enhance recovery from shale gas reservoirs. Most of the time, the pre-existing natural fractures in these reservoirs are not capable of facilitating gas production prior to stimulation. The low conductivity of the natural fracture system could be caused by occluding cements. The fact that natural fractures might be sealed by cements does not mean that they can be ignored while designing well completion processes. Cemented natural fractures can still act as weak paths for fracture growth.

In general, solutions for fluid-driven fractures are tremendously difficult to construct even for simple geometries. This difficulty is due to moving boundary conditions, non-linearity of the governing equation for fluid flow in fractures, the high gradient of displacement and pressure near the fracture tip, and non-locality of the solution. Non-linearity comes from the fact that fracture permeability is a cubic function of the fracture width. HF modeling efforts in this group are mainly focused around using extended finite element methods (XFEM) and cohesive zone methods (CZM)to solve this problem.

 

Cementing and Well Integrity

An underground blowout is Cement is used to support the casing and also provide hydraulic isolation of various formations penetrated by the wellbore, accordingly preventing fluid flow from high-pressure zone to low-pressure zones. One of the serious challenges encountered in cementing the casing in oil and gas wells is the failure of the cement sheaths and its debonding from casing or formation rock. This research group is focused on mechanical characterization of cement interfaces in the lab and sclaing up this measurements to field-scales to analyze the risk of potential broaching and other integrity problems. In parallel to studying the mechanical behavior of cement interfaces, we also research new solutions to address these problems in the form of smart polymers and graphene nanoparticles.
Horizontal drilling with hydraulic fracturing technology has played a critical role in shale revolution, while the integrity of the drilled wells have been a concern in some parts of the world. In the dogleg section of these directional wells, stiff straight casing strings should deform to fit the borehole trajectory, which lead to its complicated contact geometry in the hole. The severity of dogleg and casing properties may make the formed annulus space so complex that prevent full placement of the cement around the casing, which can endanger well integrity in some occasions. We have developed a three-dimensional large deformation models to simulate the dynamics of running a casing string into the dogleg. The deformation of casing in presence and absence of friction reducer additives have been calculated by this model to determine the annulus geometry supposed to be cemented. Then, we utilized a computational fluid dynamics (CFD) model to simulate cement displacement. Different cement rheology, pumping rates and casing specifications are considered into the developed framework to investigate the impact of incomplete or non-symmetric cement placements on fluid migration or casing failure during the next stages of field development such as hydraulic fracturing and production. Cohesive zone methods (CZM) is used to simulate the bonding between the casing and the cement sheath in different well integrity scenarios after cement placement.

Erosion and Injectivity Changes in Unconsolidated Sandstone Formations

/>The economics of water flooding projects mainly depend on large injection rates with longer injectors’ life. Frac Packs are being used increasingly in poor consolidated sands to control sands and maintain high injectivity at the injectors. Additionally, due to larger temperature differences, most deepwater injection wells will exhibit some degrees of thermal fracturing. This fracturing might be beneficial in decreasing fracture gradient and consequently improving injectivity in the short term. In the long term however, it causes a drop in injectivity. Because of undesirable and expensive well intervention later during production, a clear understanding of the physics in the vicinity of injectors is crucial to reduce water flooding costs as well as increase injection efficiency.

 

Drill Bit And Rock Interactions

The interaction of the drill bit and rock (especially in soft rocks) includes complicated progressive contact and failure mechanisms that involve ductile to brittle fracture transitions in rock with simultaneous formation of ribbons due to high confining pressure. In this research, we utilize the results generate from the existing single Cutter apparatus to incorporate it into our mechanical damage models. We plan to use experiments to investigate the underlying fracture mechanisms of rocks to formulate a Continuum Damage Mechanics (CDM) based analysis framework, which considers several physical properties including rock anisotropic damaged properties, dynamic energy density, confining pressure and temperature effects. The proposed CDM schemes already validated against a wide range of experimental data. While the classical empirical and analytical methods used for this purpose are suffering from simplistic assumptions, this work proposes a robust predictive tool for studying the rock destruction behavior under drill bit contact action, and the developed scheme may also be deployed for the drill bit optimization by incorporating the effects of the formed ribbons and bit-balling.