Cuttings transportation in coiled tubing drilling for mineral exploration

Cuttings transportation in micro-borehole annulus in coiled tubing drilling for mineral exploration was studied. The effect of cuttings size and mud properties as well as hole inclination was simulated physically using a flow loop. Computational fluid dynamics was applied to simulate lab experiments and do sensitivity analysis of various parameters. The results show significant differences in cuttings transport response in mineral exploration comparing to the oil and gas drilling applications

Design of a slurry loop for cuttings transport studies in hard rock drilling applications

Transportation of the fluid and slurry (fluid and solid particles mixture) in the pipe and annulus space has been the focus of numerous studies. There are different parameters to be considered when studying slurry transportation. These include slurry velocity or flow rates; fluid properties such as density and rheology; and solid particles properties including concentration, density, shape and size. Also the angle of the flow conduit, rotation of the pipe and possible eccentricity of the annulus are other factors which influence slurry transport characteristics. Although a number of analytical, numerical and empirical equations as well as numerical simulations have been developed for studying the flow and slurry transport, the results need to be validated against either field or lab data. As performing field tests is costly and time consuming conducting simulations at laboratory scale appears as a good alternative. Different flow loops have been designed to study the slurry transport in different science and engineering disciplines including oil and gas and mining. However, few of these consider in particular cuttings transportation in small size annulus space. The flow characteristics appear to be very different when it travels within a small size annulus, in particular when the fluid velocity is high. In this study, a review of some of the existing slurry flow loops will be conducted. Then the details of a slurry loop which has been designed and commissioned for the purpose of studying cuttings transport in a small size annulus space for applications in drilling mineral exploration wells using coil tube technology will be presented

Utilizing Coiled tube rig for mineral exploration application

Mineral exploration is in a race to employ drilling technology that can perform the exploration and drilling investigation in a fast and inexpensive manner. After an extensive study of the available drilling technologies in the market, coiled tubing was chosen as a tool to be employed for mineral exploration due to its flexible mobility and ease of operation with minimum number of personnel. Since coiled tubing technology is primarily used in oil and gas industry, it was important to re-design the coiled tube rig to drill hard rocks in a fast and feasible manner. The main requirements were to drill the smallest feasible hole diameter and go as deep in the ground as possible, in the shortest reasonable time. The drilled rock particles, cuttings, are to be collected and analysed at the surface for their metal mineral contents. The process also needs to be repeated multiple times at different locations for mapping, without the need to change the tube on the rig due to failure or potential failure. The focus of the new designed coiled tube, for drilling and mineral exploration, is three fold. First is to increase the rate of penetration (ROP) in drilling by designing a small high speed turbo motor. Second is to determine the controlling parameters of cuttings transport to effectively lift the cuttings to the surface for analysis and third is to minimize the overall weight of the rig for manoeuvring and to prolong the life span of the coiled tube string. In this paper, a small downhole turbo motor, 5cm outer diameter, is designed to achieve a rotation speed of up to 10,000 rpm to fit on a small bit, coiled tube drilling assembly. The motor design utilised multiple finite volume and finite element analysis software for fluid flow study and fluid structural interaction analysis.The paper is also introducing the concept of flow slurry loop that is designed to lift the cutting particles to the surface for mineralisation analysis. The controlling parameters of the cuttings transportation are the particles physical properties such as size, density, concentration and shape, as well as the rheological properties of the carrying fluid, drilled hole angle, as well as the fluid flow rate and flow dynamics within the annulus gap between the coiled tube and drilled hole. Such parameters are addressed via experimental work as well as numerical analysis. The paper is also presenting the selection and testing procedure of the material type for the coiled tube string. The tube needs to be light in weight for rig transportation and to drill few dozens of drill investigations holes before failing due to fatigue. A fatigue bending machine is designed to test the endurance limit of candidate materials for coiled tube string and performance index methodology is followed for material selection of the optimum material. The coiled tube rig is designed to be light in weight for transportation and relocation. It is also required to speed the drilling operation with the minimum foot print and will reclaim the drilled rock particles for mineral composition analysis at the surface

Artificial neural network model for prediction of drilling rate of penetration and optimization of parameters

According to field data, there are several methods to reduce the drilling cost of new wells. One of these methods is the optimization of drilling parameters to obtain the maximum available rate of penetration (ROP). There are too many parameters affecting on ROP like hole cleaning (including drillstring rotation speed (N), mud rheology, weight on bit (WOB) and floundering phenomena), bit tooth wear, formation hardness (including depth and type of formation), differential pressure (including mud weight) and etc. Therefore, developing a logical relationship among them to assist in proper ROP selection is extremely necessary and complicated though. In such a case, Artificial Neural Networks (ANNs) is proven to be helpful in recognizing complex connections between these variables. In literature, there were various applicable models to predict ROP such as Bourgoyne and Young’s model, Bingham model and the modified Warren model. It is desired to calculate and predict the proper model of ROP by using the above models and then verify the validity of each by comparing with the field data. To optimize the drilling parameters, it is required that an appropriate ROP model to be selected until the acceptable results are obtained. An optimization program will optimize the drilling parameters which can be used in future works and also leads us to more accurate time estimation. The present study is optimizing the drilling parameters, predicting the proper penetration rate, estimating the drilling time of the well and eventually reducing the drilling cost for future wells

Management of the disastrous underground blowout in south of Iran

An underground blowout is defined as an uncontrolled flow of formation fluids from a high to a low pressured zone. Due to the 9 5/8" casing collapse of the well no. X of MARUN Field with great tectonics, in the upper part of Aghajari Formation, Lahbari at 687 m depth, the formation oil and gas penetrated to Lahbari (with a large permeability and low formation mineral cementing) and appearing at the surface as 50 seeps (underground blowout). Most seeps were only 4 kms away from Jarahi River supplying the drinking water of three towns and additionally flows to Iran’ Largest Wildlife Refuge, Shadegan Refuge which is home to a large number of flora and fauna species. The gas was set ablaze by the emergency crew to secure the environment from gas spreading and explosion. The identification of the GPS seep coordinates and slope to the river, Construction of 31 soil dams in 3 days to accumulate oil in case of flows towards the river, establishment of a 85 m wide floating bridge after the heavy rain, application of a large number of busters, day and night operation of 1800 NISOC, UBD and emergency workers to cap the well were only part of these huge operations. Comprehensive geology, drilling and production history, incident, well capping and also especially HSE operations including future amendments would be described. Inexistent well integrity management (WIM) to monitor leakages, casing corrosion erosion, and cement quality after 34 years of production would be presented as the main reason of the blowout while. The evidence presented clearly shows the disobeyance of the contemporary drilling manager in not extending the 13 3/8” intermediate casing to 1200 m depth according to the geological well forecast. The previous 9 5/8” casing design was confirmed after designing it again

Factors affecting the gravity drainage mechanism from a single matrix block in naturally fractured reservoirs

Despite numerous experimental and numerical studies, fundamental understanding of how the matrix block height, the density difference between petroleum and gas, and matrix capillary pressure could affect the oil recovery from a single matrix block in naturally fractured reservoirs remains a topic of debate in the literature. In this work a one-dimensional gravity drainage model developed by Firoozabadi and Ishimoto (1994) is considered and numerically solved. The Fourier series method is applied for a numerical Laplace inversion of the dimensionless mathematical model; this type of inversion method has rarely been used in petroleum applications. The obtained results revealed that by increasing the matrix block height as well as the density difference between oil and gas, both the drainage flow rate and the cumulative production increased. In contrast, by increasing the matrix capillary pressure, both the drainage flow rate and the cumulative production decreased. The findings of this work can be helpful to better understand the behavior of the gravity drainage process in fractured porous media

Rheological properties and slurry behaviour in hard rock drilling

Coiled tubing (CT) drilling offers more efficient drilling operations compared to normal drilling practises resulting in lower operational costs and drilling time in oil and gas operations. This technology is recommended to be used for mineral exploration drilling in hard rock. This requires drilling micro-boreholes at very high speed with small size cuttings. A large volume of such small size cuttings can influence the rheological properties of the drilling fluids significantly. The aim of this study is to understand the effect of small size inert cuttings on the rheological properties of drilling fluids and its consequences on pressure drop changes in the annulus space. Experimental tests were performed on cuttings collected from a mining site, and the results indicated that the fluid rheology is sensitive to the cuttings size. This conclusion suggests that careful measurement of rheological properties of the mud is necessary when it is designed for drilling hard rocks

Challenges of cuttings transport in micro–borehole coiled tubing drilling for mineral exploration

Coil tubing (CT) technology has been in use in the oil and gas industry since the 1990s. Since then, the applications of CT have expanded rapidly. Coiled tube drilling can offer more efficient and faster drilling operations resulting in lower operational costs. Micro–borehole CT drilling (CTD) has been used in oil and gas applications and is very attractive as a method for minerals exploration drilling due to the faster drilling i.e. high rate of penetration (ROP) that can be achieved resulting in reduced drilling costs. Due to the narrow annulus space there is a certain degree of uncertainty with regards to cuttings transport. In this paper we review the fluid flow and cutting transport models available for conventional drilling. Different aspects of fluid flow in micro–borehole CT will be addressed and discussed. The discussion illustrates the important parameters, including fluid properties, cuttings properties, fluid hydraulics and annular geometry affecting cutting transports in micro–borehole CT drilling in oil and gas as well as mineral exploration

Investigating the influence of the variation of the load characteristic on the occurrence frequency of Grid-related Loss of Offsite Power using a probabilistic-deterministic methodology

Generic frequencies are used for Grid-related Loss of Offsite Power (GR-LOOP) in the Probabilistic Safety Analysis (PSA) of Nuclear Power Plants (NPPs). When historical databases are used, the influence of variation in the grid conditions over time and the impact of the NPP location are not considered in the estimation of GR-LOOP frequency. Therefore, relying purely on historical data induces uncertainty in total Core Damage Frequency (CDF). This paper aims at assessing the influence of the dynamic load behavior on the GR-LOOP frequency, for different locations. For that purpose, sensitivity cases are defined. The occurrence frequency of GR-LOOP following the occurrence of a three-phase-short-circuit fault on a transmission line is evaluated via a probabilistic-deterministic methodology for all cases. The minimum and maximum estimated values of the GR-LOOP frequency, 2.98E-04/year and 9.95E-03/year respectively, indicate the dependence on the variation in either the dynamic load behaviors or the NPP locations. The results reveal that GR-LOOP frequency varies with load model in the initial grid. In the presented probabilistic-deterministic methodology it is beneficial to consider the influence of timely changes of the grid conditions on the GR-LOOP occurrence frequency for different NPPs’ locations, especially where relevant or sufficient generic databases are not available.SCOPUS: ar.jinfo:eu-repo/semantics/publishe