Allan R. Rickards

Embedment and Fracture Conductivity in Soft Formations Associated with HEC, Borate and Water-Based Fracture Designs

Multi grain proppant embedment in to soft formations reduces the propped fracture width by 40% and damages the proppant pack conductivity by formation fines. Embedment and fracture width are measured for 20/40 and 40/60 mesh Ottawa gravel and 20/40 mesh sintered bauxite at proppant placement densities of 4 lb/ft 2 . The simulated formation consist of prepacked unconsolidated sand to reservoir conditions with Brinell hardness values less than 140 psi and static compaction modulus (i.e. Youngs modulus) of 200 thousand psi. The carrier fluids investigated in the embedment tests were crosslinked borate gels, linear HEC gel and high rate water packs. One to four monolayers of proppant embedment were measured at two leakoff rates corresponding 0.01 and 0.03 ft/root-min. The embedment test results were measured with a sensitive electronic micrometer and confirmed by microphotography. Proppant pack conductivity tests were also performed to determine the damage associated with formation fines at two closure stresses of 2000 and 5000 psi. At 5000 psi closure stress, 10% formation fines can reduce pack conductivity to only 18% of the original pack conductivity at 2000 psi. Embedment increases with increased proppant size (i.e. embedment 20/40>40/60 mesh), closure stress (i.e. embedment 5000 psi > 1000 psi) and fluid viscosity (i.e. embedment borate > HEC). To maintain fracture width and conductivity, stimulation treatments should be designed for a minimum of 4 lb/ft 2 . Fractures with propped widths of 2 lb/ft 2 are essentially closed and have very low conductivity due to formation fines damage.

Increased Resistance to Proppant Flowback by Adding Deformable Particles to Proppant Packs Tested in the Laboratory

Numerous proppants, additives and remedial treatments now exist for the control of proppant flowback, yet it continues to be a problem in many oil and gas wells. These approaches to the problem can have certain merits but as a general rule they negatively impact production and are more costly than proppant alone. The importance of these criteria must be balanced against the effectiveness of the chosen approach. It has been observed in laboratory testing that a deformable proppant material, blended with a typical fracturing proppant. can significantly increase a proppant packs resistance to failure under flowing conditions The fluid exerts a drag force on the structure of the pack and indeed on the individual particles within. These drag forces appear to be much less than the overburden forces that maintain a proppant pack in a stable configuration, prior to fluid flow. In essence proppant packs of typical fracture width, when tested in the laboratory are inherently unstable, unless the individual particles within are anchored or reinforced in some way. When a deformable proppant is blended into the pack, the deformation between the surrounding proppant grains allows locking of these grains in place. The friction between the grains is effectively increased and thus, the forces required to push the material out of the structure also increase. Addition of deformable particles typically allows the drag forces at failure to be increased by 100% to 300%, while pack conductivity remains better or on a par with the proppant alone, since the material added does not adversely reduce porosity.

Need Stress Relief? A New Approach to Reducing Stress Cycling Induced Proppant Pack Failure

Stress cycling of proppant packs often occurs during well production operations and is known to be a major contributing factor to proppant pack failure. Proppant crushing occurs due to increasing closure stress as a well is drawn down. The fines generated by such crushing can cause significant damage to proppant pack porosity and fracture conductivity. Additionally, the incidence of proppant flowback (fines and whole proppant) has been reported to be exacerbated by stress cycling. The addition of deformable beads to the proppant pack has been observed to alleviate both problems and may significantly improve well performance. Testing of various mixtures of the deformable beads and proppant has demonstrated significant reductions in the amount of fines generated and accompanying improvements in proppant pack permeability. Furthermore, the initiation of proppant flowback was observed to require much higher flow rates than in the absence of the beads. It is thought the process of bead deformation serves to cushion the proppant particles from the full brunt of the stress. New laboratory facilities and procedures have been established to study and quantify proppant flowback, and conductivity as a function of proppant, temperature, flow rate, fracture width, closure stress, and cycle frequency.

Analyzing Cements and Completion Gels Using Dynamic Modulus

The measurement and control of the physical properties of completion fluids are important problems to the oil and gas industry. A new laboratory instrument, a dynamic modulus analyzer (DMA), has been developed that analyses the physical and mechanical properties of fluids and cement slurries under downhole conditions by using high resolution ultrasonics. A dynamic modulus analyzer can measure compressive strength, dynamic Young`s modulus, and the shrinkage or expansion of cements. The DMA can also be used to determine viscosity changes and changes in the density of fracturing and completion gels under static (10{sup -4} s{sup -1}) or zero shear conditions. Test data indicate the DMA is 20 to 100 times more sensitive than current laboratory instruments in evaluating changes in cements or gel properties. Cement shrinkage was measured simultaneously with compressive strength and dynamic modulus. The times required to achieve maximum gel strength and gel breaking were also determined for Fracturing gels and a temporary blocking gel.