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Log response comparison between wire-line logging from vertical and horizontal branch well (Well X3-H2) and LWD (Well X3-H1) Table 1 Parameter comparison between wire-line logging of vertical intervals and LWD of horizontal intervals, Zone 1, Well X3 Vertical well X3 (wire-line logging) Horizontal well X3-H1 (LWD logging) Zone No. GR/ API
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The effect of drilling fluid invasion on the resistivity of oil-bearing zones during the period from penetrating the zone to completion well logging was studied using intergraded logging while drilling (LWD) and wire-line log data. The results indicate that resistivity change during invasion responds to some important factors such as porosity, oil...
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... compared. Well X3 consists of one vertical well and two horizontal branch wells. LWD runs in the vertical well and horizontal branch well of Zone 2 (X3-H2), and wire-line logging runs in the horizontal branch well of Zone 1 (X3-H1). Log data from Well X3 are used to compare the log responses between LWD and wire-line logging, which are shown in Fig. 2 ...
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... Schematic view of instrumented drill rigs and wireline logging in blastholes or dedicated holes Example of logging while drilling data and wire-line logging used in petroleum geomechanics(Zhongyuan et al. 2010) ...
This study proposes an improved method for accurately characterising rock masses to
optimise the design of differential blasts. The authors focus on identifying key technologies
and approaches for obtaining and delivering the necessary information for blast design. They
suggest technical pathways for further development, testing, and validation to address the
identified challenges. Four potential groups of approaches are identified, each consisting of
specific techniques for different types of ore:
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exposed areas of the bench.
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dedicated sensing holes.
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areas of the bench.
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capabilities (e.g., cross-hole seismic) determining various rock mass characteristics in the
bench.
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techniques that consider different mechanical parameters of rocks. Grade indicates the areas
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The drilling fluid invasion into hydrate-bearing sediments (HBS) would trigger geological risks. However, invasion mechanisms and formation responses during drilling the gas hydrate reservoirs, especially the fluid-loss characteristics and control mechanisms of hydrate dissociation, remain poorly understood. Thus, we develop a three-dimensional (3-D) coupled thermal-hydro-chemical model to investigate the drilling fluid invasion process and dynamic responses of gas hydrate reservoirs. This model deals with the fluid-loss and flow field characteristics as well as well-formation interactions considering the effect of hydrate dissociation. The results indicate that the invasion characteristics mainly depend on drilling fluid pressure and permeability, while the temperature influences the hydrate dissociation. Besides, the fluid-loss velocity increases slowly after a sharp decrease at initial stage of invasion due to the increase of permeability induced by hydrate dissociation. Afterward, characteristics and mechanisms of drilling fluid invasion into hydrate reservoirs are determined by the invasion process coupled with hydrate dissociation. Given the unique characteristics of HBS, the invaded formation is divided into flushed zone, transition zone, and undisturbed zone, presenting a better description of the dynamic filtration process. Moreover, optimization strategies and drilling technology are proposed to prevent hydrate dissociation and control geological risks during drilling hydrate.
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Horizontal wells can significantly improve the gas production and are expected to be an efficient exploitation method for the industrialization of natural gas hydrates (NGHs) in the future. However, the near-wellbore hydrate is highly prone to decomposition during the drilling process, owing to the disturbance aroused by the factors such as the drilling fluid temperature, pressure, and salinity. These issues can result in the engineering accidents such as bit sticking and wellbore instability, which are required for further investigations. This paper studies the characteristics of drilling fluid invasion into the marine NGH reservoir with varied drilling fluid parameters via numerical simulation. The effects of the drilling fluid parameters on the decomposition behavior of near-wellbore hydrates are presented. The simulating results show that the adjustments of drilling fluid density within the mud safety window have limited effects on the NGH decomposition, meanwhile the hydrates reservoir is most sensitive to the drilling fluid temperature variation. If the drilling fluid temperature grows considerably due to improper control, the range of the hydrates decomposition around the horizontal well tends to expand, which then aggravates wellbore instability. When the drilling fluid salinity varies in the range of 3.5–7.5%, the increase in the ion concentration speeds up the hydrate decomposition, which is adverse to maintaining wellbore stability.
... The dissociation rate primarily depends on the circulation rate of drilling fluid. Afterward, the variation of measured resistivity was obtained to reflect the invasion process and penetration depth in tests [28,29], which can provide a reference for resistivity logging during drilling natural gas hydrate reservoirs. Also, experiments on drilling in hydrate-bearing sediments were carried out to investigate the invasion characteristics and physical responses of sediments, which reflects the interactions between the drilled well and formation [23,27,30]. ...
To solve the problem that it is difficult to identify carbonate low resistivity pays (LRPs) by conventional logging methods in the Rub Al Khali Basin, the Middle East, the variation of fluid distribution and rock conductivity during displacement were analyzed by displacement resistivity experiments simulating the process of reservoir formation and production, together with the data from thin sections, mercury injection and nuclear magnetic resonance experiments. In combination with geological understandings, the genetic mechanisms of LRPs were revealed, then the saturation interpretation model was selected, the variation laws and distribution range of the model parameters were defined, and finally an updated comprehensive saturation interpretation technique for the LRPs has been proposed. In the study area, the LRPs have resistivity values of less than 1 Ω·m, similar to or even slightly lower than that of the water layers. Geological research reveals that the LRPs were developed in low-energy depositional environment and their reservoir spaces are controlled by micro-scale pore throats, with an average radius of less than 0.7 μm, so they are typical microporous LRPs. Different from LRPs of sandstone and mudstone, they have less tortuous conductive paths than conventional reservoirs, and thus lower resistivity value under the same saturation. Archie's formula is applicable to the saturation interpretation of LRPs with a cementation index value of 1.77—1.93 and a saturation index value of 1.82—2.03 that are 0.2—0.4 lower than conventional reservoirs respectively. By using interpretation parameters determined by classification statistics of petrophysical groups (PGs), oil saturations of the LRPs were calculated at bout 30%—50%, 15% higher than the results by conventional methods, and basically consistent with the data of Dean Stark, RST, oil testing and production. The 15 wells of oil testing and production proved that the coincidence rate of saturation interpretation is over 90% and the feasibility of this method has been further verified.
Fractured tight sandstone gas reservoirs were characterized with narrow pore throats, developed natural fractures, abundant clay minerals, and local ultra-low water saturation, geologic characteristics make those tight reservoirs inclined to strong potential damages. Drill-in fluid may easily invades reservoirs along fractures due to the long soaking time and an overbalanced pressure differential, causing serious formation damage and affecting the economic and efficient development of tight gas reservoirs. An integrated multidisciplinary method was pursued in this paper to accurately evaluate the damage extent of drill-in fluid to tight gas reservoirs. The techniques involve different drill-in fluid damage evaluation methods including core analysis, well logging interpretation, the numerical simulation, and well testing analysis. Results show that the average permeability damage rate through natural flowback after HTHP dynamic damage of drill-in fluid in matrix samples (68.45%–70.70%) were much higher than of fracture samples (44.37%–52.28%). The calculation results of resistivity logging data show that the average filtration invasion depth of drill-in fluid was 1.25 m and the median cumulative filtration invasion depth was 1.26 m. When the simulated bottom hole differential pressure was 3.5 MPa and the simulated soaking time was 150 h, the filtration invasion depth of drill-in fluid was 1.30 m and the lost circulation invasion depth of drill-in fluid was 6.34 m. Afterwards, taking the permeability damage rate and invasion depth as the bridges, the damage skin factor was calculated through Hawkins formula, and the calculated results were in good agreement with the decomposition of well testing results. Finally, an integrated multidisciplinary and multiscale comprehensive evaluation method of drill-in fluid damage in fractured tight sandstone gas reservoirs was proposed, which can serve as a guide for the drill-in fluid damage evaluation in fractured tight gas formation.
Downhole electromagnetic transmitter is an important part of EM-MWD system, which can send low-frequency EM waves data from a downhole tool to surface in real time for oil and gas exploration. In order to reduce the volume and weight of the downhole electromagnetic transmitter and improve the depth and accuracy of petroleum exploration, a novel downhole electromagnetic transmitter topology for electromagnetic MWD system is designed. Aiming at the complex and changeable characteristics of load impedance of transmitter, an equivalent load model for downhole electromagnetic transmitter is established with drill string, casing, drill-bit, drilling fluid and formation being taken into account. Because the attenuation characteristic of electromagnetic signal in the wellbore is similar to that of capacitor discharge, the characteristic of electromagnetic channel can be equivalent to the combination of capacitance and resistance. Then, in order to ensure that the downhole electromagnetic transmitter will produce the nominal load voltage, irrespective of disturbances such as variations in the lithium batteries voltage, perturbations in the switching times, and the load, a dual-loop real-time feedback control scheme with an outer voltage loop and an inner current loop is proposed. Simulation and experimental results with laboratory prototype demonstrate the effectiveness of the control method for downhole electromagnetic transmitter. It also ensures the downhole electromagnetic transmitter's excellent stability and the accuracy of the established equivalent load model as well as its ability to meet the requirements of practical field deep exploration. The findings of our work can help for better understanding of approximate load model of downhole electromagnetic transmitter. Furthermore, it will be of great significance for designing control algorithm of downhole electromagnetic transmitter for different areas or boreholes, achieving the purpose of increasing transmission depth. The research results can be used to improve the design and optimization of electromagnetic MWD measurement system in the aspects of improving the control accuracy of the transmitter, saving energy and increasing the transmission depth.
Rock cores are important for rock properties research because they are linked to significant oil and gas drilling and production technology around the world. The goal of synthesising rock cores in the laboratory is to simulate the main factors of properties of reservoir rocks such as permeability, porosity and pore radius that can be used for tests in extreme conditions in replacement the high cost of obtaining natural cores. The reproduction of artificial rock cores in the laboratory also enables researchers to obtain samples with predetermined characteristics to better understand the relationship between their physical characteristics. In this paper, low-permeability and high-porosity artificial rock cores were made by 3D printing technology. The behaviour of the main petrophysical characteristics of these samples was investigated, such as setting time, rheology, permeability, porosity and compressive strength. The results were compared with natural samples and showed a high similarity to the petrophysical behaviour. By optimising the ratio of 3D printing materials, the physical properties of the samples were closer to the natural carbonate rocks. It provides a new technique and method to the development of special reservoir physical simulation experiments.
Drilling fluid invasion into hydrate-bearing sediments could induce hydrate dissociation and complicate heat and mass transfer around wellbore, and further affect mechanical strength of hydrate-bearing sediments and accurateness of wellbore logging interpretations. In this study, a cylindrical numerical model was established to study the characteristics of drilling fluid invasion into hydrate-bearing sediments and the effects of permeability on this process. The distributions of temperature, pressure, saturation, and salinity of pore water around wellbore at different time were obtained. The pressure and temperature around wellbore gradually increase, and the hydrate around wellbore dissociates with the high-temperature drilling fluid invasion. Meantime, water and gas generated from hydrate dissociation gradually migrate outward and then form ‘secondary hydrate’ in some areas outside wellbore. Dissociation and formation of hydrate can sharply change the salinity of pore water around wellbore. The drilling fluid invasion and hydrate dissociation ranges become larger when the intrinsic permeability is higher. The salinity in sediments decreases sharply while the dilution range is narrow when drilling fluid invasion into hydrate-bearing sediments with low permeability. In addition, the permeability decline exponent of the Masuda model has a significant influence on drilling fluid invasion. However, the Corey exponents of the relative permeability model only have a limited influence on drilling fluid invasion into hydrate-bearing sediments with low intrinsic permeability (e.g., 5.5 mD), while they have a noticeable influence on hydrate-bearing sediments with high intrinsic permeability (e.g., 75 mD).
