The study here presents laboratory testing results of Class F fly ash geopolymer for oil well cementing applications. The challenge reported in literature for the short thickening time of geopolymer ash has been overcome in this study, where more than 5 h of the thickening time is achievable. API Class H Portland cement used a controller on all the tests conducted in this work. Tests conducted in this research include unconfined compressive strength (UCS), shear bond strength, thickening time, shrinkage, free water, and cyclic and durability tests. Results indicate temperature as a crucial factor affecting the thickening time of geopolymer mix slurry. UCS testing indicates considerably higher compressive strength after one and fourteen days of curing for geopolymer mixtures. This indicates gaining strength with time for geopolymer mixture, where time retrogression effects are observed for Portland cements. Results also indicate higher shear bond strength for geopolymer mix that can better tolerate debonding issues. Additionally, more ductile material behavior and higher fracture toughness were observed for optimum geopolymer mixes. Tests also show applicability of these materials for deviated wells as a zero free water test was observed.
Lost circulation has been a serious problem while drilling that may lead to heavy financial costs in the form of lost rig time and lost mud fluid. In severe cases, it can lead to well blowout with serious environmental hazards and safety consequences. Despite extensive advances in the last couple of decades, lost circulation materials used today still have disadvantages such as damaging production zones, failing to seal large fractures or plugging drilling tools. Here, we propose a new class of smart expandable lost circulation material (LCM) to remotely control the expanding force and functionality of the injected LCM. Our smart LCM is made out of shape memory polymers that become activated by formation's natural heat. Once activated, these particles can effectively seal fractures' width without damaging pores in the production zone or plugging drilling tools. The activation temperature of the proposed LCM can be adjusted based on the formation's temperature. We conducted a series of experiments to measure the sealing efficiency of these smart LCMs as a proof of concept study. Various slot disk sizes were used to mimic different size fractures in the formation. The API RP 13B-1 and 13B-2 have been followed as standard testing methods to evaluate this product.
In real time drilling, the complexity of drilling fluid filtration is majorly attributed to changing mud rheology, formation permeability, mud particle size distribution (PSD), filter cake plastering effects, and geochemical reaction of particles at geothermal conditions. This paper focuses on quantifying the major effects as well as revealing their contribution toward effective wellbore stabilization in sandstone formations. We conducted an extensive experimental and analytical study on this subject at different levels. First, we used field application and the results as guides for our experiments. We have considered both oil-based mud and water-based mud. Next, we optimized the mud particle size distribution (PSD) by carefully varying the type, size, and concentration of wellbore strengthening material (WSM). Laboratory high pressure high temperature fluid loss tests were carried out on Michigan and Bandera Brown sandstones. The results from these tests identify the formation heterogeneity and permeability in successful wellbore stabilization. Filter cake permeability calculations, using the analytical model for linear systems, were consistent with filtration rates, and the expected trend of permeability declines with time. Finally, we investigated the evolution of internal filter cake and plastering mechanism, using scanning electron microscopic (SEM) analysis. The test results revealed a significant difference in the formation permeability impairment for the optimal mud PSD and WSM blend.
Filtrate and solid invasion from drilling fluids are two key sources of formation damage, and can result in formation permeability impairment. Typically, spurt invasion of mud solids causes the evolution of an external mud cake which tends to reduce further solids and filtrate influx. However, uncontrolled spurt and filtrate invasion are detrimental because they reduce the permeability of the formation. Mud composition, formation rock's permeability and porosity, and temperature can influence both spurt and filtrate invasion. The sizes of mud solids relative to the average pore size of a rock are also important in predicting the extent of mud invasion and permeability impairment. In this paper, a dynamic modeling approach is presented for mud solids deposition on the pores of rock samples for different lithologies. The modeling results were compared to experimental values. To simulate a close-to-real field mud invasion and damage scenario, rock samples were first subjected to a dynamic-radial fluid loss test under controlled laboratory conditions. The geometry of the simulated drill pipe and inner diameter of the cores allowed for uniform mud cake evolution around the wall of the cores. Three different rock samples (Michigan sandstone, Indiana limestone, and Austin chalk) were investigated. Two water-based mud (WBM) samples were formulated to simulate high and low fluid loss recipes. Next, scanning electron microscopy (SEM) imaging of the dry cores coupled with image processing was used to determine the porosity and pore size distribution of the internal mud cake. The structure of the porous rocks as well as the mud cake were modeled using the bundle of curved tubes approach. In addition, the deposition probability of mud solid particles was considered through filtration theories. Experimental results showed up to 40% reduction in mud invasion and damage to the rocks using the low fluid loss recipe. The model developed in this study closely matched the experimental results. The model revealed a maximum relative error of about 9.6% for one out of the six case studies, and an average relative error of 3.3% for other case studies. The novelty in this study is the quantitative utilization of SEM images by applying watershed segmentation algorithm to detect and measure the size of mud cake pore spaces. This approach can be implemented in the design of drilling fluids that can reduce formation damage.
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