Lab-Scale Permeability Enhancement by Chemical Treatment in Fractured Granite (Cornubian Batholith) for the United Downs Deep Geothermal Power Project, Cornwall (UK)

A hydrothermal doublet system was drilled in a fault-related granitic reservoir in Cornwall. It targets the Porthtowan Fault Zone (PTF), which transects the Carnmenellis granite, one of the onshore plutons of the Cornubian Batholith in SW England. At 5058 m depth (TVD, 5275 m MD) up to 190 °C were reached in the dedicated production well. The injection well is aligned vertically above the production well and reaches a depth of 2393 m MD. As part of the design process for potential chemical stimulation of the open-hole sections of the hydrothermal doublet, lab-scale acidification experiments were performed on outcrop analogue samples from the Cornubian Batholith, which include mineralised veins. The experimental setup comprised autoclave experiments on sample powder and plugs, and core flooding tests on sample plugs to investigate to what degree the permeability of natural and artificial (saw-cut) fractures can be enhanced. All samples were petrologically and petrophysically analysed before and after the acidification experiments to track all changes resulting from the acidification. Based on the comparison of the mineralogical composition of the OAS samples with the drill cuttings from the production well, the results can be transferred to the hydrothermally altered zones around the faults and fractures of the PTF. Core Flooding Tests and Autoclave Experiments result in permeability enhancement factors of 4 to >20 and 0.1 to 40, respectively. Mineral reprecipitation can be avoided in the stimulated samples by sufficient post-flushing.

Numerical Simulation of Effective Hole Cleaning by Using an Innovative Elliptical Drillpipe in Horizontal Wellbore

In the drilling of horizontal wells, the drill cuttings tend to settle down on the low side of the annulus due to gravity and form a stationary bed, which results in hole cleaning problems. In this paper, a novel type of drillpipe with an elliptical shape was proposed to alleviate inadequate hole cleaning during the drilling of horizontal wells. A three-dimensional computational fluid dynamic (CFD) Eulerian-Eulerian approach with the Realizable k-ɛ turbulence model was developed to predict the solid–liquid two-phase flow in the annular space. Numerical examples were given to investigate the influence of different parameters on cuttings’ transport behavior, and the elliptical drillpipe was compared with the circular drillpipe. The annular cuttings concentration, annular pressure drop, and hole cleaning efficiency were evaluated. The numerical results clarify the potential of the elliptical drillpipe to enhance the hole cleaning efficiency without significantly increasing the annular pressure drop. Due to the swirl flow and secondary flow caused by the rotation of the curvature wall, the swaying phenomenon of drill cuttings’ distribution along the rotation direction of drillpipe was observed and enhanced the cuttings transport ability. Using the elliptical drillpipe as a joint-type tool can improve hole cleaning performance. Under the optimum conditions applied in this study, the hole cleaning efficiency increased by nearly 18%.

The Determination of the Methane Content of Coal Seams Based on Drill Cutting and Core Samples from Coal Mine Roadway

The determination of methane content of coal seams is conducted in hard coal mines in order to assess the state of methane hazard but also to evaluate gas resources in the deposit. In the world’s mining industry, natural gas content in coal determination is usually based on direct methods. It remains the basic method in Poland as well. An important element in the determination procedure is the gas loss that occurs while collecting a sample for testing in underground conditions. In the method developed by the authors, which is a Polish standard, based on taking a sample in the form of drill cuttings, this loss was established at a level of 12%. Among researchers dealing with the methane content of coal, there are doubts related to the procedures adopted for coal sampling and the time which passes from taking a sample to enclosing it in a sealed container. Therefore, the studies were designed to evaluate the degree of degassing of the sample taken in the form of drill cuttings according to the standard procedure and in the form of the drill core from a coal mine roadway. The results show that the determinations made for the core coincide with the determinations made for the drill cutting samples, with the loss of gas taken into account.

Using on-stream X-ray fluorescence analysis to determine the chemical composition of drill cuttings

Background. The authors investigate the problems arising from the lack of information on the chemical composition of the drilled rocks during the construction of a well. Aim. The aim of this study is to determine the possibilities and efficient application of the streaming XRF method for determining the elemental composition of unwashed drill cuttings. The contribution of the paper lies in the lack of experience in the world practice of using streaming XRF analyzers. Materials and methods. Furthermore, the authors evaluate the possibility to use the streaming XRF method for analyzing the chemical composition of drill cuttings for the development of the oil industry. At the same time, the application of the proposed method is justified. The basis of this study are the results of the application of the streaming XRF method using the CON-X 02 streaming spectrometer for analyzing the chemical composition of drill cuttings not washed from drilling mud. This project has been implemented according the technological project between Gazpromneft — NNGGF LLC in cooperation with Nosov Magnitogorsk State Technical University and Gazpromneft — STC LLC. Result. The article presents the results of determined main elements of the composition of drill cuttings. The authors have carried out the analysis of changes in the intensity of the characteristic lines of the main components from the sampling depth. Simultaneously, the authors show the possibilities to derive correlation curves for various elements characteristic of certain rocks in the geological section of a particular field. Moreover, the study reveals the identification and characteristics of geochemical signs of specific target layers. Conclusions. Based on the results of the study, authors may conclude that to obtain the correct results on the intensity of spectral lines of various chemical elements during streaming XRF analysis, there is no need to flush the cuttings from the drilling fluid. Finally, it is possible to qualitatively control the main elements of the composition of the drill cuttings.

A Comparative Emissions Assessment - Drill Cuttings Treatment Alternatives

The offshore industry has for many years been cognisant of its impact on the marine environment. Since 1991, strict regulations relating to oil-based drill cuttings discharge have been in force in the signature countries to the OSPAR (Oslo/Paris) Convention. As the impact of greenhouse gas (GHG) emissions on climate change has become better understood, global carbon dioxide (CO2) emission reduction targets and how to meet them have risen up operators’ agendas. Offshore operations, which involve marine logistics, are also subject to limits on nitrogen dioxide (NOx) emissions, an indirect GHG that's toxic to humans and contributes to soil and water acidification. The choices that operators make today in how they operate, including the disposal of drill cuttings, must therefore address an increasing number of environmental and climate targets, in addition to health, safety and cost. This paper will outline the results of a comparative study between the offshore processing of drill cuttings and relevant conventional alternatives, including skip and ship, bulk transfer and cuttings reinjection (CRI). It is the first paper to show a direct emissions comparison between offshore processing and all other alternative methods for drill cuttings processing. The study assessed the carbon footprint and NOx emissions for each of the different alternatives for the treatment of drill cuttings. The values were then used to create an interactive emissions calculator that can be easily applied to specific projects to clarify the actual potential for emissions reduction within the drilling waste management process. A number of case studies were then run, comparing the different alternatives. For the examples run, the comparative assessment showed that wellsite thermal processing technology was the favourable alternative in terms of emissions, with an emission reduction in the order of 14 - 48%, compared with the onshore alternatives. Emissions of the alternatives, skip and ship and bulk transfer, were highly dependent on sailing and road transport distances, as well as power source for the onshore treatment facility. The assessment showed that CRI has the highest emissions of CO2 per tonne of cuttings. Alternatives involving onshore treatment had the highest NOx emissions when sailing distance was high, however this was highly dependent on the machinery and fuel source of the transport vessel - and for the offshore alternatives, the on-site energy production solution.

Estimating Water Content in Water-oil Mixtures and Porous Media they Saturate: Joint Interpretation of NMR Relaxometry and Dielectric Spectroscopy

The article is devoted to the topical problem of estimating water content in water-oil mixtures and porous media they saturate, according to low-field NMR relaxometry and dielectric spectroscopy. The aim of the research is to theoretically substantiate and experimentally validate the capability of joint interpretation of data from these methods to acquire information on the filtration-volumetric properties of drill cuttings, relaxation characteristics of oil-containing fluids, water/oil ratio in water-oil mixtures and saturated with them drill cuttings in order to control the composition of liquids produced from boreholes. The studies were carried out on samples of cuttings and oils taken from fields in the northern and Arctic regions of the West Siberian oil-and-gas province. Based on the experimental data obtained, we evaluated the water content in the water-oil mixtures, determined the main NMR parameters of the mixtures in terms of properties of the constituent oils, and specified the parameters and shapes of NMR and complex dielectric permittivity spectra. The NMR method was found to be effective in examining high-viscosity and medium-viscosity oils, while the dielectric spectroscopy method – in the study of light oils; their integration allows obtaining reliable data for all the samples under study. We also showed how the shapes of NMR and complex dielectric permittivity spectra depend on the rheological properties of oil belonging to the mixture.