An experimental study of permeability determination in the lab

Understanding the flow characteristics in laminar and turbulent flow regime is important for different aspects of reservoir and production engineering. One of the most important parameters in fluid flow is the permeability of the porous media. It is common practice in the industry to use Darcy and Forchheimers equations for characterising the fluid flow in the porous media at laminar and turbulent regimes, respectively. Core flooding experiments were performed with 1.5-inch diameter size core samples from limestone and sandstone formations. The permeability of the samples was measured in the laminar regime at basis flow rate. Then, the flow rate was increased in different steps and permeability was measured, accordingly. The plot of permeability versus flow rate was used to track the evolution of the flow regimes in the core porous media. There are different challenges to monitor the transition between laminar and turbulent regime through core flooding experiments. These challenges are discussed in this paper through both literature review and also experimental results. The results indicated that the core sample preparation, experiment control parameters and also test profiles are important aspects when measuring permeability in the lab. © 2012 WIT Press

Bridging performance of new eco-friendly lost circulation materials

Lost circulation is one of the most important concerns of the drilling industry, causing excessive expenditure and increasing the non-productive drilling time. In this study, various lost circulation materials (LCMs) were used to control the lost circulation of two types of drilling fluids, bentonite mud and a new eco-friendly mud, named RIA-X, which has a remarkable effect on decreasing the amount of lost circulation in fractured and highly permeable reservoirs. The Bridging Material Test (BMT) apparatus was used to investigate the effectiveness of various LCMs in fractures of various sizes and to select the LCM and combination with the best performance. The use of three-dimensional fractures is one of the most notable points of this work, which makes the experimental conditions similar to those of real wells. The lost control performance of the new eco-friendly LCMs in RIA-X mud was tested in field. The outcomes show that the designed LCMs are able to control severe lost circulation that regular processes such as cementing or drilling with foam cannot deal with

Drilling response of impregnated diamond bits: modelling and experimental investigations

The research aims to develop bit/rock interaction models for Impregnated Diamond (ID) bits. An experimental approach is used to study the dominant cutting and wear processes governing the bit/rock interface. The developed models are used to investigate the effects of the bit and rock properties as well as operating conditions on the drilling response. Furthermore, a field case study is performed, at which the drilling data is analysed using the framework of the model

The wear mechanisms of impregnated diamond bits

Impregnated diamond (ID) bits are rotary drag bits, which are specifically dedicated to drill hard and abrasive rock formations. Performing like a grinder wheel, the cutting face ID bits is continuously evolving during drilling, exposing new and sharp diamonds. The performance and the life of these bits are thus controlled by an integrated and complex wear process. To better understand the wear mechanisms of ID bits, a series of drilling and cutting tests were conducted with ID core bits and segments at CSIRO's Drilling Mechanics Laboratory. The results have indicated that the evolution of ID cutting face is characterized by different patterns or wear mechanisms, depending on the depth of cut imposed. At shallow depth of cuts, the wear is predominantly dominated by diamond polishing and erosion of the binder, and at higher depth of cuts, the wear is controlled by diamond fracturing and matrix abrasion

Drilling response of impregnated diamond bits: An experimental investigation

The use of impregnated diamond (ID) bits has dramatically increased in hard and abrasive drilling environments over the last few decades. Although frequently used, the drilling performance of ID bit is still quite volatile and inconsistent. The dissipation of energy at the bit/rock interface is postulated as a combination of two independent processes: pure cutting or fragmentation and friction across wear surfaces. In order to better understand the mechanisms governing the bit/rock interaction, it is necessary to isolate the processes mobilised across the interface. This paper deals with the steady-state drilling response of ID bits, also called "stationary" response, in other words, the relationship between forces acting on the bit and depth of cut under conditions of constant wear state. A series of tests is performed with crowns/segments and bits on four different granites and one sedimentary limestone, using two kinematic controlled drilling rigs. The results have shown that the cutting response varies through three linear regimes that are characterised by different dominant mechanisms acting at the interface. The results also indicate how the micro-properties of the rock such as mineralogy and the segment properties (matrix hardness, wear status, concentration and diamond size) affect the response. Copyright 2013 ARMA, American Rock Mechanics Association

The development of a new sonic correlation for UCS estimation from drilling data

One of the most important characteristics of rocks in drilling operations is unconfined rock strength (UCS), which is critical in different aspects of drilling operations. Several laboratory-based correlations have been generated for specific rocks to estimate UCS from physical properties (such as transient time, porosity, and Young's modulus) of the rocks. In drilling analysis, when UCS information is required and direct methods for estimation of UCS are not available, it is common to use correlations that have been developed for other formations with the same or similar lithology. Obviously, the results of estimations based on UCS correlations for other formations will not be accurate and can affect subsequent analyses. Therefore, it is highly recommended to generate a correlation for the formation of interest, though it is not always possible to reach this goal from experimental works on core samples retrieved from the formation. In this study, a sonic correlation that shows that it can provide relatively better global estimation of UCS for limestone rocks is modified for one of the Iranian carbonate formations by determining new coefficients for the correlation based on drilling data. For this purpose, the drilling information recorded in mud logging data is analyzed to backward simulate the drilling process based on a modified penetration rate model and calculate the rock strengths of the formation. The apparent rock strength log generated from this calculation proceeds quality-controlled steps according to statistical and pattern recognition methods to eliminate the noises and fluctuations that normally exist while working with field data. Then, a new correlation is developed from the formation response to sonic logs and apparent rock strength log. Because this new correlation is originally generated for the formation of interest, UCS is estimated more accurately and analyses dependent on UCS show fewer errors. Copyright © Taylor & Francis Group, LLC

Effect of groove geometry and cutting edge in rock cutting

© 2017 Elsevier B.V. The purpose of this paper is to investigate the effects of rock/cutter interface geometry on the cutting action of a circular sharp Polycrystalline Diamond Compact (PDC) cutter tracing a groove on the surface of a rock sample. A series of laboratory cutting experiments are carried out on two sedimentary rocks (a limestone and a sandstone) using a state of the art rock scratch device. The results confirm that the magnitude of the cutting force is directly correlated to the cross-sectional area of the groove. However the results also show that the shape or geometry of the groove and in particular the length of the cutter's edge in contact with the rock, affect both the magnitude and the inclination of the force acting on the cutter. Further investigation revealed, even a sharp cutter is not perfectly sharp due to microscopic imperfections distributed along the cutters edge. Results further show that the effect of the cutter's edge can vary strongly from on rock material to another; while the effect is found negligible when carrying test in the sandstone, it is of first order in the limestone

Numerical simulation for the determination of hydraulic fracture initiation and breakdown pressure using distinct element method

Hydraulic fracturing technique has been widely used in many cases to enhance well production performance. In particular, this technology is proven to be the most viable technique for the oil and gas production from unconventional reservoirs. Accurate prediction of fracture initiation and breakdown pressure is vital for successful design of Hydraulic Fracturing operation. Methods of predicting these pressures include analytical analysis, field experiments, laboratory experiments and numerical simulations. Despite great achievements in the area of analytical analysis, they often failed to represent the true reservoir case, and consequently are found to be erroneous. Field tests such as mini-frac test are the best method for prediction of initiation and breakdown pressure. However these tests are very limited due to their costs and are not very suitable for sensitivity analysis. Controlled laboratory tests seem to be the best option for predicting initiation and breakdown pressures. Test parameters such as fracturing fluid properties and principal stresses can be controlled with great precision to achieve accurate results. However, same as field tests, laboratory experiments are expensive. Core samples are limited and are expensive. Coring operation can take 4-5 days of rig time to take a 90 ft core. Geo-mechanical tests can take up to three days of a laboratory technician's time per sample. Consequently, this will limit the number of tests to be done, and as a result it causes limitations on the conclusions that can be drawn from these tests. Simulation studies on the other hand do not have these limitations and can be used for as many times as desired to perform sensitivity analysis.This paper presents a simulation model that is based on distinct element method. It is used to study the fracture initiation and breakdown pressure during hydraulic fracturing tests. The accuracy of the model was justified through comparison between laboratory experiments and numerical simulation. Four sandstone samples from two different sandstone types and a synthetic cement sample were used in the experimental studies. The tests were performed in True Tri-axial Stress Cell (TTC) with the capability to inject fluid into the samples. Simulation results demonstrate good agreement with experimental results. Fracture propagation path was found to be very similar. Fractures propagated in the direction of maximum horizontal stress

Wear response of impregnated diamond bits

© 2018 Elsevier B.V. The drilling response of impregnated diamond (ID) bits is controlled by processes involved in the rock fragmentation, and also the wear processes that continuously change the bearing surface of diamonds and bonding matrix. Due to the co-existence of these two processes both affecting the overall drilling response but differently based on drilling conditions (operating parameters, bit, rock and drilling fluid), the response of ID bits has been found inconsistent and difficult to interpret. In this paper, wear mechanisms of impregnated diamond bits are studied using a series of precise state of the art cutting and drilling experiments conducted with impregnated diamond bits and segments. The wear responses are decomposed into three phases of polishing, fracturing and sharpening, and the response in each phase is analyzed using interface laws in terms of depth of cut, and the extents of frictional contacts. The variation of the response at various operating parameters (weight on bit and depth of cut) are obtained and conceptual models characterizing the drilling response under both weight-on-bit and depth of cut conditions are presented