Field Drilling Research Articles

Laboratory simulation of change in mechanical and flow properties of reservoir formations at various stages of oil-field development

At various stages of the development of oil and gas fields, the formation experiences various stress-strain states. Changes in reservoir pressure during development lead to changes in the physical and mechanical properties of the reservoir. The properties of the host rocks are also influenced by the fluids themselves. The process of extracting formation fluid can cause not only clogging of the filtration channels with leached rock particles and precipitation of paraffins and salts, but also a decrease in the strength and elastic characteristics of the rock. The article provides a brief analysis of the works affecting the causes of changes in the physicomechanical and filtration-reservoir properties of reservoirs during drilling and development of oil fields. The technique of theoretical calculation of changes in porosity and permeability of formations is given. To establish the convergence of theoretical calculation methods with real data, tests were carried out to determine the tensile strength under uniaxial compression and filtration experiments on terrigenous samples of one of the fields in Western Siberia. In an experiment to determine the physicomechanical properties, water and kerosene in various proportions were used as saturation liquids. Based on the data obtained, the dependences of the elastic modulus and tensile strength under uniaxial compression on various types of saturation were derived, graphs and calculation formulas are presented. In the filtration experiment with volume compression, the effect of the effective pressure on the permeability of the samples was determined. The dependences of the decrease in permeability on the axial load on the sample are established. The obtained dependencies can be used in the preparation of geological and technical measures for stimulation of inflow and in the management of field development throughout the entire life cycle.

Seismic fine imaging and its significance for natural gas hydrate exploration in the Shenhu Test Area, South China Sea

ABSTRACT Shenhu area in South China Sea includes extensive collapse and diapir structures, forming high-angle faults and vertical fracture system, which functions as a fluid migration channel for gas hydrate formation. In order to improve the imaging precision of natural gas hydrate in this area, especially for fault and fracture structures, the present work propose a velocity stitching technique that accelerates effectively the convergence of the shallow seafloor, indicating seafloor horizon interpretation and the initial interval velocity for model building. In the depth domain, pre-stack depth migration and residual curvature are built into the model based on high-precision grid-tomography velocity inversion, after several rounds of tomographic iterations, as the residual velocity field converges gradually. Test results of the Shenhu area show that the imaging precision of the fault zone is obviously improved, the fracture structures appear more clearly, the wave group characteristics significantly change for the better and the signal-to-noise ratio and resolution are improved. These improvements provide the necessary basis for the new reservoir model and field drilling risk tips, help optimize the favorable drilling target, and are crucial for the natural gas resource potential evaluation.

Advanced prediction for field strength parameters of rock using drilling operational data from impregnated diamond bit

Abstract Field drilling can be a continuous, fast, and reliable technology to predict the cohesion, internal friction angle, and unconfined compressive strength (UCS) of rock in petroleum engineering. Herein, a theoretical model is established in an impregnated diamond bit considering some effective parameters including friction parameter, crushed zone, and bit geometry parameter. A novel method is proposed to determine field strength parameters including the cohesion, internal friction angle, and UCS of four types of rock using drilling logging data. Many drilling experiments in the field are conducted using a drilling process monitoring apparatus to obtain drilling logging data (thrust force, torque, penetration rate, and rotation speed). Experimental results on weak, medium-strong, and strong rock show that drilling with an impregnated diamond core bit includes two fully dependent and simultaneous processes: rock cutting and frictional contact, the dominant role of which is dependent on the cutting point. The cohesion, internal friction angle, and UCS estimated from the proposed method for the four types of rocks are close to those from standard laboratory tests. This practical method can provide practical, fast, and reliable estimation for field strength parameters of rock and should be highly beneficial to field applications in rock engineering.

A REVIEW OF NANOTECHNOLOGY APPLICATIONS IN THE OIL AND GAS INDUSTRIES

Nanotechnology encompasses the science and technology of objects with sizes ranging from 1 nm to 100 nm. Today, exploration and production from conventional oil and gas wells have reached a stage of depletion. Newer technologies have been developed to address this problem. Maximum oil production at a minimum cost is currently a huge challenge. This paper reviews nanotechnology applications in the oil and gas production sector, including in the fields of exploration, drilling, production, and waste management in oil fields, as well as their environmental concerns. The paper reviews experimental observations carried out by various researchers in these fields. The effect of various nanoparticles, such as titanium oxide, magnesium oxide, zinc oxide, copper oxide, and carbon nanotubes in drilling fluids and silica nanoparticles in enhanced oil recovery, has been observed and studied. This paper gives a detailed review of the benefits of nanotechnology in oil exploration and production. The fusion of nanotechnology and petroleum technology can result in great benefits. The physics and chemistry of nanoparticles and nanostructures are very new to petroleum technology. Due to the greater risk associated with adapting new technology, nanotechnology has been slow to gain widespread acceptance in the oil and gas industries. However, the current economic conditions have become a driving force for newer technologies.

A REVIEW OF NANOTECHNOLOGY APPLICATIONS IN THE OIL AND GAS INDUSTRIES

Nanotechnology encompasses the science and technology of objects with sizes ranging from 1 nm to 100 nm. Today, exploration and production from conventional oil and gas wells have reached a stage of depletion. Newer technologies have been developed to address this problem. Maximum oil production at a minimum cost is currently a huge challenge. This paper reviews nanotechnology applications in the oil and gas production sector, including in the fields of exploration, drilling, production, and waste management in oil fields, as well as their environmental concerns. The paper reviews experimental observations carried out by various researchers in these fields. The effect of various nanoparticles, such as titanium oxide, magnesium oxide, zinc oxide, copper oxide, and carbon nanotubes in drilling fluids and silica nanoparticles in enhanced oil recovery, has been observed and studied. This paper gives a detailed review of the benefits of nanotechnology in oil exploration and production. The fusion of nanotechnology and petroleum technology can result in great benefits. The physics and chemistry of nanoparticles and nanostructures are very new to petroleum technology. Due to the greater risk associated with adapting new technology, nanotechnology has been slow to gain widespread acceptance in the oil and gas industries. However, the current economic conditions have become a driving force for newer technologies.

Numerical modelling and field experimental validation of the axial load transfer on the drill-strings in deviated wells

Abstract This paper studies the axial load transfer along the drill-strings in deviated wells by developing a finite element model based on the Euler beam theory and the augmentation Lagrangian contact algorithms. The model can simulate the entire drill-strings showing nonlinear contact model between drill-strings and casing. Special attention is given to the axial load loss, the pipe-casing contact force distribution and the slender pipe deformation. The efficacy of the proposed model is validated experimentally using a packer releasing procedure. Various drill-string factors, such as deviation angle, dogleg severity, hook load magnitude and buckling configurations, are considered for evaluating the efficiency of axial load transfer. Our analysis shows that the dogleg severity has a significant influence on the transfer, and the helical buckling of the drill-strings due to excessive loading could make it worse. This study provides a theoretical understanding of the variation of the contact force and the axial load transfer for the drill-strings in deviated wells. It can be used to better understand the working condition of downhole and guide field drilling.

Large-scale and high-similarity experimental study of the effect of drilling fluid penetration on physical properties of gas hydrate-bearing sediments in the Gulf of Mexico

Abstract In this study, the process of drilling fluid penetrating into gas hydrate-bearing sediments in the Gulf of Mexico Hydrate Joint Industry Project was simulated with conditions similar to in situ drilling process parameters and reservoir temperatures and pressures. Natural sediments were replaced by artificial sediments columns with approximately similar physical properties. The temperature, pressure, and resistivity were measured in real time, and the effects of drilling fluid penetration on the physical properties were analyzed. The hydrate saturation, penetration depth, and influence mechanism of temperature and pressure difference were obtained. By orthogonal analysis, the porosity and resistivity of the artificial sediments columns were found to be optimized closely to natural conditions, with a difference of 1.29% and 4.0%, respectively. During penetration, a positive pressure difference was useful for maintaining hydrate stability, while the temperature difference had an opposite influence. High density, low temperature, and low filtration loss drilling fluid were found to be beneficial for field drilling. Hydrate decomposition gradually occurred with increasing depth, accompanied by reformation. The front edge of resistivity lagged behind the pressure and temperature, with a depth of ~0.65 m. Therefore, for resistivity logging after drilling, logging methods with a coordinated detection depth should be considered; thus, a dual laterolog with deep focused resistivity measurements would be a better choice.

Early Cambrian syndepositional structure of the northern Tarim Basin and a discussion of Cambrian subsalt and deep exploration

Abstract Using field geological survey, drilling and seismic data, combined with the study of regional tectonic evolution and structural deformation, as well as lithological and sedimentary analysis, we reconstructed the basin filling process and paleo-geography of north Tarim Basin in Early Cambrian, aiming to analyze the factors controlling the distribution and spatial architecture of the subsalt reservoir and source units and to define the favorable exploration direction. The Late Sinian tectonic activities in the northern Tarim Basin were characterized by different patterns in different areas, which controlled the sedimentary pattern in the Early Cambrian. The boundary faults of Nanhuaian rift basin in the south slope of Tabei uplift and the north slope of Tazhong uplift became reactivated in the Early Cambrian, forming two NEE and EW striking subsidence centers and depocenters, where the predicted thickness of the Yurtusi Formation could reach 250 meters. In the Xiaoerbulake period, the weak rimmed platform was developed in the hanging wall of syndepositional fault. Whereas the Nanhuaian rift system in the Tadong and Manxi areas were uplifted and destroyed in the Late Sinian, and appeared as gently slope transiting toward the subsidence center in the Early Cambrian. The former had the sedimentary features of hybrid facies platform and the latter had the sedimentary features of ramp platform. The black shale of the Yurtus Formation in the footwall of syndepositional fault and the reef bank of Xiaoerbulake Formation platform margin in the hanging wall in Early Cambrian constitute a predicable source-reservoir combination. The activity intensity of syndepositional fault controlled the thickness of black shale and the scale of the reef bank. It is suggested carrying out high accuracy seismic exploration to determine the location of Early Cambrian syndepositional faults, on this basis, to search the reef bank of Xiaoerbulake Formation along the faults westward, and then drill risk exploration wells at sites where traps are shallow in buried depth.

CO2-water-rock predictions from aquifer and oil field drill core data: The Precipice Sandstone-Evergreen Formation CO2 storage reservoir-seal pair

SummaryThe Surat Basin is one of the most prospective onshore basins in Australia for CO2 storage. The Precipice Sandstone and Evergreen Formation have been appraised for their feasibility as a future CO2 storage reservoir-seal pair. Here we will focus on predicted CO2-water-rock reactions. These predictions rely on mineral and porosity data from drill core. Data were obtained from northern and two southern regions of the Basin. The northern region was more data rich. The southern region is more well core and data sparse with the exception of the Moonie oil Field. Additional drill core samples were collected from archived well core of Moonie and other parts of the basin. The core samples were characterised for porosity, mineral, and metal content to build geochemical models to predict local CO2-water-rock reactions and their potential effect on reservoir scaling, changes to porosity and mineral trapping of CO2. For the northern region, our work has predicted low reactivity of the Precipice Sandstone, with mineral trapping in the Evergreen Formation. The Precipice Sandstone sampled in the Moonie field has different mineralogical characteristics to wells in the Northern region. Here, CO2-water-rock predictions indicate minor alteration of plagioclase and K-feldspar to kaolinite, chalcedony and ankerite in cleaner Moonie sandstones, with additionally precipitation of smectite in clay rich sands. Formation water pH was buffered between 5 and 6 by dissolution of calcite or siderite cements. Sampled core has also shown evidence of previous natural CO2 and hydrothermal fluid alteration, fractured quartz grains, and fracture fills with mineral trapping as carbonates. This type of natural analogue data is vital to validate long term predictions. New drill core and data are still required in future for the southern and central Surat Basin region which is most prospective for CO2 injection and storage.

Large‐scale experiments of the borehole instability on shale formation influenced by drill pipe rotation

AbstractWellbore instability happens mostly in the shale formation. Early researches have studied thoroughly on the physicochemical and mechanical mechanism that causes instability. However, only a few works have considered the influence of field drilling operations, such as drill pipe rotation. In this paper, a true triaxial cell is used to simulate the downhole field situations, and a drill pipe rotation device is innovatively designed and implemented into the true triaxial cell. Using this facility, the influence of drill pipe rotation on shale instability has been performed. Different rotation speed, weight on bit, drilling fluid pressure, and microcracks on borehole have been considered. The enlargement of the wellbore is quantitatively plotted and compared. Results show that the drill pipe rotation contributes to a more enlargement of the wellbore, and a higher rotation speed causes a more severe collapse. The drill string weight on bit also contributes to the enlargement of the wellbore, with a larger weight on bit induces a larger diameter of the collapsed wellbore. Compared with the rotation speed and weight on bit, the influence of drilling fluid density is relatively less significant. However, the influence of microcracks caused by hitting of drilling tools is profound. For a cracked shale formation, the wellbore diameter can be enlarged for more than 40%. Then, the variation of borehole collapse with time and depth under drill pipe rotation influence is analyzed. In all of these four factors, the significant sequence is microcracks > weight on bit > rotation speed > drilling fluid pressure. In all the collapse phenomena, the collapse is more severe in the minimum horizontal stress direction. This is explained by the analysis of the stress distribution in the whole circumferential angle (360°) of the wellbore. Overall, this work fills the gap of the influence of drilling operations on wellbore instability.

Synergetic System for Water Body Detection in Coal Mine: A Case Study

Detection of water yield property is one of the most important tasks for mine water control. Because of low reliability of a single water detection method, it is necessary to find an effective water detection system. In this study, we established a circulatory system for water detection (CSWD) and analyzed working principles of each module of the system. The system was then tested in a China coal mine, and the detailed arrangement of the system was discussed. The geophysical detecting results show that there were three abnormal areas with abundant water body (i.e. safe area I, dangerous area II and potentially dangerous area III). The possibility of those areas initiating water hazards varied a lot. The precautionary and danger areas were verified by field drilling. The drilling results indicate that the amounts of water in most holes of areas II and III were large and the largest water amount reached approximately 63 m3/h. Sites occurring of water inrush accorded well with the detection results using the CSWD, indicating that the CSWD is effective and reliable in detecting areas with potential water hazards.

Abrasion Rule of Polycrystalline Diamond Compact Bit Cutter

To decrease polycrystalline diamond compact (PDC) cutter abrasion and improve the PDC bit’s drilling performance, based on the academic analysis, a series of rock cutting experiments were made on a lathe with a single PDC cutter to understand better the effects of cutting angle, height of protrusion, linear velocity and the indentation hardness on PDC cutter wear. By the experiments, it shows that the different cutting angles are suitable to different heights of protrusion; for example, the optimal protrusion height of PDC bit with cutting angles of 25° is 3 mm. Also, the PDC abrasion volume and the linear velocity are found to be in direct proportion during well drilling operations, and the PDC abrasion volume can be obtained by the formula V = δμpFvt. Besides, the PDC cutter’s abrasion volume is in inverse proportion to indentation hardness. It is suggested to select the PDC bit with larger cutting angle when drilling the rock samples with larger indentation hardness and select the smaller cutting angle when drilling the soft formation. Field drilling tests of five bits with different cutting angles are conducted to verify the validity of the laboratory tests. The drilling experiment results agree with the results obtained by the laboratory tests. The results of this study can be applied to each PDC cutter on a given bit; then, the contributions of every cutter can be integrated to determine the bit performance. Also, this study can serve as a guidance for developing new PDC bit design that are optimized for specific rock formations.

The subseafloor thermal gradient at Iheya North Knoll, Okinawa Trough, based on oxygen and hydrogen isotope ratios of clay minerals

Abstract We measured the oxygen and hydrogen isotope ratios of smectite, chlorite, and illite in hydrothermally active sediments at the Iheya North Knoll, Okinawa Trough, obtained by seafloor drilling of active hydrothermal fields during the Integrated Ocean Drilling Program (IODP) Expedition 331. Formation temperatures calculated from oxygen isotope data were compared to the downhole temperatures that were measured during the same expedition. The δ18O values ranged from +9.9‰ to +13.3‰ for smectite, +1.3 to +3.0‰ for chlorite or chlorite/smectite mixed-layer mineral, and +2.1‰ to +5.1‰ for illite or illite/smectite mixed-layer mineral with minor chlorite. For samples of illite that contained minor chlorite, δ18O values for illite or illite/smectite mixed-layer mineral of +4.4‰ to +6.1‰ were calculated, based on the proportion of the two clay minerals calculated from chemical composition of the individual mineral and the mixture determined by TEM-EDS and EPMA. We estimated the formation temperatures of the minerals using oxygen isotope fractionation data and assumed values of 0 to +1.2‰ for the fluid that was equilibrated with the minerals, based on the reported values of the seawater and vent fluid measured in previous studies. The temperature range calculated was 111–175 °C for a shallow layer less than about 25 m below seafloor (mbsf) that contained smectite and a minor kaolinite component, 177–297 °C for a deeper layer between about 25 and 40 mbsf that was dominated by chlorite or chlorite/smectite mixed-layer mineral, and 220–314 °C for the deepest layer between about 40 and 120 mbsf that contained illite or illite/smectite mixed-layer mineral with less chlorite. The temperatures of mineral formation calculated from the oxygen stable isotope data were slightly higher at some depths, but both calculated and measured temperatures demonstrated a steep, step-wise thermal gradient below the active hydrothermal field, where temperatures of >200 °C were determined at as little as 50 mbsf. Hydrogen isotope values mostly ranged between −40 and −55‰ and did not vary significantly or systematically between the layers, except in the clay fractions containing smectite above 25 mbsf that had relatively low values between −65 and −72‰. Hydrogen isotope results of the clay minerals were problematic to interpret and not consistent with interpretation of the oxygen data. Calculated temperatures from illite and smectite were mostly negative, whereas temperatures calculated from chlorite were more positive (average 145 °C), but lower than those from the oxygen isotope data. Additional work is still required to determine the hydrogen isotope fractionation between clay minerals and water with respect to temperature.

The 25 Years of Experience Since Inauguration of All-Russian Center for Disaster Medicine “Zaschia” (Protection)

Introduction:Main functions of the Russian Federation in disasters and emergencies are loaded on All-Russian Center for Disaster Medicine of Ministry Health (ARCDM). The principal strategies of the staff are to play leading roles in preparedness, emergency response, evacuation, recovery of health systems, and education.Methods:Our presentation includes selection, classification, analysis, and statistics. There about 80 territorial Disaster Medicine Centers working under the leadership of ARCDM. One experience from the Moscow Territory Disaster Medicine Center will be presented.Results:At the operational and informational department, there are nine special medical emergency teams (three with helicopters). Time of arrival takes between seven and ten minutes, and transport to the hospital takes about five to seven minutes with 33 landing places for helicopters. The operational and control department uses an early warning system. About 1,300 exercises were organized in these centers and hospitals. We will discuss the examples of medical care delivery to the injured in metro Slaviynskie, Basar park Pobedi, Narofominskay, two major fires, and hurricanes. The mobile field hospital worked in more than 12 countries and in many territories in the Russian Federation over 25 years.Discussion:The last year was very difficult due to the Football World Cup, working hard as a collaborating center in emergencies, and working in the framework of a memorandum with China. Preparedness for an international event next May, which includes a field drill with participants from emergency medical teams of Health Ministries of CIS Countries and from State Health of China. We invite others to observe or join this event. Thus, we have some difficulties and problems, but we must increase solidarity and collaboration due to the scale, frequency, and number of losses in emergencies and disasters. Humanity could be able to cope with emergencies if we take into account these issues.

Improved natural state simulation of Arjuno-Welirang Geothermal field, East Java, Indonesia

Arjuno-Welirang Geothermal Field is a green field located across Mojokerto Regency, Malang Regency, Pasuruan Regency and Batu City in East Java Province, Indonesia. Geothermal system in Arjuno-Welirang Geothermal Field is estimated to be liquid dominated and has a reservoir temperature of about 260°C based on CO2 gas geothermometry method. Several manifestations are found at the surface; consist of hot springs, fumaroles and alterations. The field is now managed by Geo Dipa Energi. Geological, geophysical, and geochemical studies have been conducted in the field but exploration drilling has not been carried out yet until recently. For reservoir characterization and resource estimation purposes, several conceptual models have been developed based on available geoscience data. Previously, a natural state modelling attempted to match existing conceptual models has been carried out by Wardana. An entirely new natural state numerical model is made in this study to improve the result from previous model by using smaller grid blocks (40% finer). In return, the result shows more accurate temperature matching of surface manifestations than the previous model. The numerical model is developed using TOUGH2 simulator to obtain natural state condition. The objectives of this study are to develop an improved natural state numerical model; to validate temperature of the manifestations in the model with measured manifestation data; to characterize geothermal reservoir including area, thickness, pressure, temperature and permeability distribution; and to determine resource potential using probabilistic method. All data used in this paper are based on published papers.

Design and numerical analysis of a large‐diameter air reverse circulation drill bit for reverse circulation down‐the‐hole air hammer drilling

AbstractReverse circulation down‐the‐hole (RC‐DTH) air hammer drilling is a fast and cost‐effective method for hard rock drilling. As the air RC drill bit is the heart for RC‐DTH air hammer drilling system to form the reverse circulation, a large‐diameter RC drill bit was innovatively designed and numerically optimized with respect to the suction ability. Results show that increasing the suction‐nozzle elevation angle and deflection angle can improve the drill bit suction ability. The drill bit performance reaches its optimal state when the air flow rate was about 1.205 kg/s, thereafter it exhibits a reverse variation trend with the increase in air mass flow rate. The optimum diameter of the suction nozzles is 20 mm for the drill bit studied in this work. The RC drill bit with outer diameter of 665 mm and RC‐DTH air hammer with outer diameter of 400 mm were manufactured and a field trial was conducted. Field test results show that the penetration rate using the RC‐DTH air hammer drilling method is more than twice the conventional rotary drilling method. This drilling approach poses a great potential for the large‐diameter hard rock drilling applied in the upper portions of a well bore above the potential producing reservoir formation for land oil and gas drilling, geothermal drilling and relevant field drilling operations.

The Geophysical Response of the Tupinda Cu-Au-Mo Porphyry Prospect, Tabar Islands, Papua New Guinea

The Tupinda porphyry prospect is located in the Tabar Islands Group of Papua New Guinea (PNG), approximately 80 km NW of the supergiant Lihir epithermal gold deposit (43 Moz Au). Geophysical data over the prospect include airborne magnetics and radiometrics, ground pole-dipole induced polarization and resistivity, gradient array induced polarization, petrophysics, and airborne time domain electromagnetics. All geophysical datasets clearly identify the footprint of the porphyry body and associated alteration system. The magnetic data show a central high representing the magnetite altered potassic core surrounded by a circular zone of low response indicative of magnetite destructive alteration. The radiometric data show a discrete potassium anomaly overlapping the magnetic anomaly. The pole-dipole IP data display a resistive chargeable zone coincident with the magnetic anomaly. Mid to late time airborne EM data exhibit a broad sub-circular resistor coincident with the mapped limits of the alteration system. Field mapping and drilling of the prospect are consistent with the geophysical data. Outcropping potassic alteration is observed at the location of the magnetic and radiometric anomalies. Drill core shows widespread disseminated sulphide mineralization consistent with the chargeable response observed in the IP data. Predominantly fresh felsic lithologies intersected in the drilling concur with the resistor measured in the airborne EM data. A more complex relationship exists between grade (Au and Cu) and magnetic susceptibility, with some areas displaying a good correlation and other demonstrating a more cryptic relationship which may be a function later overprinting geological events.

Assessment of rock strength from measuring while drilling shafts in Florida limestone

The focus of this research is the real-time assessment of rock strength (unconfined compressive strength, qu) during drilled shaft installations in Florida limestone, where measures of rock strength are provided through five monitored drilling parameters: torque, crowd, rotational speed, penetration rate, and bit diameter. To complete the study, both a laboratory and field investigation were required. This paper covers drill rig instrumentation, measuring rock strength during field drilling, and the comparative analysis of rock strength with conventional methods. Real-time measurements were recorded for each drilling parameter and graphically displayed on an in-cab monitor and wirelessly transmitted to an external computer. Measures of rock strength were estimated using a laboratory-developed equation with the monitored drilling parameters for real-time field assessment. Measuring while drilling in the field took place at three separate locations where drilled shaft load testing occurred. Comparative analyses between the monitored shaft installations and core samples subjected to unconfined compression indicated the results aligned well when recoveries were good. As recoveries diminished, the mean strengths were comparable, but more variable.

Investigation into the performance of asphalt mixture designed using different methods

Abstract To investigate the performance of asphalt mixture designed by the vertical vibration method, the vertical vibration design method (VTM design method) and Marshall design method were used to design the AC-16 (asphalt concrete with nominal maximum aggregate size = 16 mm) asphalt mixture. The physical properties, mechanical properties, road performance and fatigue property of the asphalt mixture designed by these two methods were examined. The results show that compared with that of the Marshall method, the optimal asphalt content of the asphalt mixture designed by the VTM method is decreased by 9.0%, and the density is increased by 1.8%; the mechanical properties, anti-rut ability and anti-crack ability are increased by at least 30%, 34% and 17%, respectively; and the water stability is also improved slightly. In addition, the fatigue life can be increased by at least 59%. The results also show that the Marshall stability, compression strength, splitting strength, tensile strength and shear strength of field drill cores designed by the VTM method are increased by at least 42%, 32%, 21%, 31% and 33%, respectively, compared with those of the Marshall method. Clearly, the performance of the asphalt mixture designed by the VTM method is better than that of the Marshall method, which could offer a better choice for asphalt mixture design.

A solids-free brine drilling fluid system for coiled tubing drilling

Abstract There are many problems associated with coiled tubing drilling operations, such as great circulation pressure loss inside pipe, difficulties in weight on bit (WOB) transferring, and high probability of differential sticking. Aiming at these problems, solids-free brine drilling fluid system was developed on the basis of formulation optimization with brine base fluid experiment, which was evaluated and applied to field drilling. Based on the optimization of flow pattern regulator, salt-resisting filtrate reducer, high performance lubricant and bit cleaner, the basic formula of the solids-free brine drilling fluid system was formed: brine + (0.1%−0.2%) NaOH + (0.2%−0.4%) HT-XC + (2.0%−3.0%) YLJ-1 + (0.5%−2.0%) SDNR + (1.0%−2.5%) FT-1A + (1.0%−5.0%) SD-505 + compound salt density regulator. Lab evaluation showed that the fluid had satisfactory temperature resistance (up to 150 °C), excellent cuttings tolerance (up to 25%), and strong inhibition (92.7% cuttings recovery); Moreover, its lubrication performance was similar to that of all oil-based drilling fluid. The wellbore could be fairly cleaned at annular up-flow velocity of more than 0.8 m/s if the ratio of yield point to plastic viscosity was kept above 0.5. This fluid system has been applied in the drilling of three coiled tubing sidetracking wells in the Liaohe Oilfield, during which the system was stable and easy to adjust, resulting in excellent cuttings transportation, high ROP, regular hole size, and no down hole accidents. In summary, the solids-free brine drilling fluid system can meet the technical requirements of coiled tubing drilling.