1,720,967 research outputs found
Rheology and Corrosivity of Drilling Fluids Formulated from Al-Ghatt Saudi Clays
No full textAn experimental investigation has been carried out to determine the rheological and corrosive properties of Al-Ghatt clay, when used as a basic constituent for drilling fluid, on mild steel and J-55 steel alloys normally used in oil and gas wells casing fabrication. The study was extended to investigate the effect of a sodium hydroxide (NaOH) addition on the corrosive properties. Corrosion rates were measured under both static and dynamic conditions at 15% by weight clay concentration and with the addition of various concentrations of sodium hydroxide (NaOH). Under the static conditions, the maximum corrosion rate was found to vary from zero to 73.25 mil-inch/year. Under dynamic conditions, however, a maximum corrosion rate of 155.3 mil-inch/ year and a minimum of 0.125 mil-inch/year was detected. The results showed that the resistance to corrosion of the steel alloys is very good at high alkalinity drilling fluids in both static and dynamic conditions. Based on the rheological and corrosivity tests, drilling fluids formulated from Al-Ghatt clay are suitable for oil and gas wells drilling as long as the concentration of the NaOH is maintained at 1% by weight
Relationship between Reservoir Productivity and Pore Pressure Drop
No full textThe significance of permeability sensitivity to changes in pore pressure (i.e., to change in effective overburden stress) has been examined by modifying Darcy law for radial single-phase steady state flow. The elaborate model accounts for pore pressure drop and permeability reduction due to reservoir compaction. Three Saudi oil reservoir rock samples as well as Berea sandstone were tested for their physical properties. All of these cores were free of microfractures. Furthermore, using 1% NaCl aqueous solution, relationship between the overburden pressure and absolute permeability of these samples were determined at several levels of confining pressure at which the permeability was calculated. These tests were performed to establish the effect of reservoir depressurization on reservoir rock permeability.The experimental work performed in this study showed that reservoir rocks of high initial porosity and permeability are highly affected by reservoir (pore) pressure drop and resulting increase in the effective stress. For example, the production rate from sandstone sample N3 decreased 25% of its initial value when the pore pressure decreased by 25% of its initial value, whereas the production rate from carbonate sample N4 decreased 8% for the same pore pressure decrease. Moreover, it was observed that the reservoir rock permeability under in-situ conditions strongly depends on its initial porosity and permeability values. This study suggests that a severe error in productivity predictions can result on assuming that the formation permeability at depth is independent of the effective stress. Because the increase in the effective stress decreases porosity which, in turn, changes permeability
Simple Correlation to Evaluate Mohr-Coulomb Failure Criterion Using Uniaxial Compressive Strength
No full textThe evaluation of Mohr-Coulomb failure criterion as well as other mechanical properties for reservoir rocks is essential for well planning, development and characterization of oil and gas reservoirs. This is because the understanding of the rock-stress relationship can solve many reservoir problems and avoid cost of remedial work. For example, a Mohr-Coulomb failure criterion may be used for borehole instability analysis, water injection design, production optimization techniques, compaction and sand production prediction, etc.A Mohr-Coulomb failure criterion is a function of the apparent cohesion (τ0) and the angle of internal friction (φ). The evaluation of these two parameters requires testing of many rock samples using an expensive and time-consuming triaxial testing set-up. In this study, a correlation between the apparent cohesion and the uniaxial compressive strength was developed. It is based on laboratory data of more than 200 rock samples of different types obtained from the literature. The correlation coefficient of the developed correlation equals to 0.82. Verification of the developed correlation using data from other references has shown an average error of estimation equal to 10%. Therefore, the Mohr-Coulomb failure criterion’s parameters as well as Poisson’s ratio can be estimated using the developed correlation based on fast and cheap measurements of the uniaxial compressive strength
Prediction of Critical Pipe Running Speed During Tripping in Drilling Operations
No full textBlowout and loss of circulation are two serious accidents that can happen while drilling without the control on drillstring running speed during tripping operations. Exceeding the critical running speed during tripping-out (high swabbing pressure) and lack of control of mud rheology are the main causes for blowout. Also, exceeding the critical running speed while tripping-in (high surge pressure) and lack of control of mud rheology are the main causes for loss of circulation. Many factors which affect surge and swab pressures must be precisely selected in order to control kicks or blowouts and to prevent loss of circulation. Prediction of the critical pipe running-in and -out speeds during tripping operations is therefore very important. This can be done by the evaluation of several basic fluid flow equations. A computer program has been developed to simplify these calculations. The developed program requires fairly simple input data which can be measured in laboratory in addition to hole and drillstring dimensions. The output of this program then is transformed into graphical form from which the safe running-in and -out speeds during tripping can be predicted. As an alternative and direct way to predict the critical pipe running speed during tripping operations two correlations have been developed. These correlations account for the governing factors which affect the tripping-in and -out speeds including mud properties and drillstring and hole configuration. A comparison between the critical pipe running speed computed using the two methods has been outlined and very good accuracy based on the coefficient of linear correlation (r2) and the standard error of estimate (SEE) (r2 = 0.995 ; SEE = 0.39 for running-out correlation and r2 = 0.875 ; SEE = 0.817 for running-in correlation) have been obtained. Critical tripping speeds were found to be greatly dependent on mud weight and rheology, hole diameter and drillcollars-to-drillpipe length ratio
Characterization of Shale-Drilling Fluid Interaction Mechanisms Related to Wellbore Instability
No full textWellbore stability problems tend to occur during the drilling phase in shale sections, hence the understanding of shale-drilling fluid interaction mechanisms is essential if wellbore instability is to be avoided when drilling through shale sections. A review on the origin of shale electric potential is presented in this paper. Simple tests to be used at rig-site to characterize shale reactivity in the presence of drilling fluids were developed. These developed tests were verified by means of developing easy to use equipment made especially for this study. Borehole collapse problems that occur when drilling in shale sections were simulated using thick-walled shale cylindrical specimens. It was found that any increase in sample moisture content has led to a reduction in shale strength and decreased borehole stability, while the increase in wellbore pressure was found to improve borehole stability
A Laboratory Study of Factors Affecting Primary Cement Sheath Strength
No full textAn investigation of factors affecting cement sheath strength has been carried out.. This study performed on hardened (cured for seven days) cement specimens. These specimens were prepared by mixing 35% fresh water by weight of dry Portland cement (class A according to API classification or C 150 type I according to ASTM classification) plus various percentages of Thumama sand (5-40% by weight of dry cement). The relationship between cement tensile and compressive strengths as well as cement direct and indirect tensile strenghs have been established. Factors affecting cement-casing and cement-formation shear bond strength were studied. Cement compressive and tensile strength were correlated to each other as well as to the cement shear bond strength. It was found that casing surface roughness, casing surface cleaning and casing centralization have enhanced the strength of cement-casing shear bond, whereas the deposition of mud cake on the wall of the simulated borehole has reduced the strength of cement-formation shear bond
Estimating the Amount of Free Sand in the Yielded Zone Around Vertical and Horizontal Oil Wells
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Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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