Marcin Kremieniewski

Energy demand and growing environmental concerns have fueled increased interest in geothermal drilling in recent decades. The high temperature and pressure in the boreholes present significant challenges to drilling, particularly in terms of the selection of suitable drilling mud, cement slurry, and drilling equipment. Drilling mud is regarded as one of the primary factors that affect the cost and success of geothermal drilling. This paper presents experimental studies aimed at assessing the thermal stability of drilling muds for geothermal drilling. Research on the antidegradation of polymers contained in drilling muds is presented. The thermal stability of drilling fluids was evaluated on the basis of changes in rheological and filtration parameters under the influence of a temperature of 160 °C. Attempts were made to increase the thermal resistance of drilling fluids by using antioxidants and glycol compounds. The effectiveness of increasing the thermal resistance of muds by adding synthetic polymers, nanomaterials, and graphite was tested. A new way of increasing the thermal resistance of drilling muds by using fatty amine compounds in combination with the amine agent ‘TEA’ was proposed. Tests showed that the addition of polyglycol and the antioxidant agent sodium ascorbate to the mud did not protect the polymers from decomposition at 160 °C. There was no effect of increasing the thermal conductivity on improving the thermal resistance of the scrubber. Based on the analysis of results from laboratory tests, a composition of a water-based drilling mud without bentonite was developed for drilling geothermal wells. The developed drilling mud is characterized by thermal resistance up to 160 °C, stable rheological parameters, low filtration, and appropriate thermal conductivity characteristics.

Ensuring proper and effective cementing of casing pipe columns in boreholes requires maintaining appropriate technological parameters for the developed slurry recipes. It is also necessary to use technology which guarantees effective displacement of the drilling mud for cement slurry injection into the annular space of the borehole. The most important factors that ensure high efficiency of drilling mud displacement by the cement slurry are, among others, the rheological properties of the liquids involved in the process of cementing the casing columns (drilling mud, cement slurry, buffer liquid). The introduced version of the European cement standard, PN-EN 197-1, includes new types of very economical multi-component cements CEM V/A and CEM V/B, which contain 20–40% Portland clinker with a relatively high content of hydraulic and pozzolanic constituents. They occur in the form of granulated blast furnace slag, natural as well as industrial pozzolans and silica fly ash from the combustion of hard coal. The article presents the results of laboratory tests on the technological parameters of both fresh and hardened cement slurries prepared on the basis of CEM V multi-component cement varieties A and B. These slurries meet the standard technological parameters to a demanding extent, which makes it possible to apply them to cementing columns of casing pipes in deep hole drilling. Their detailed properties can be modified by introducing other mineral additives and chemical admixtures to the cement slurry recipes.

Ensuring effective sealing of casing columns in boreholes requires the use of the appropriate technology of cement slurry injection into the annular space and the use of a properly designed cement slurry recipe. Very often, when selecting the technological parameters of the cement slurry, special attention is paid to the technological parameters of the fresh cement slurry, but little attention is paid to the mechanical parameters of the cement sheath that is being formed (the cement slurry after setting). In order to improve the parameters of the hardened cement slurry in the annular space, the cement slurry of a new generation with increased durability (so-called geopolymers) is used. Slurries based on geopolymers are obtained by modifying slurries based on common-use cements with mineral additives with pozzolanic or hydraulic properties. Most often, these additives are fly ashes from the combustion of hard coal or ground granulated blast furnace slags. The article presents the results of testing the mechanical parameters of hardened cement slurries prepared on the basis of CEM V multi-component cement. It was found that the increase in the amount of silica fly ash in the slurry causes a delay in the strength growth rate; such slurries have lower values of early strength. The water–cement coefficient has the strongest influence on the mechanical parameters. The test results are also statistically developed, thanks to which it is possible to select the appropriate mathematical model, and this enables the prediction of mechanical parameters for slurries as a function of their hardening time. Such a mathematical solution can save some labor-intensive research, which, however, cannot be omitted in the final stage of slurry design.

Every year, the number of exploited mine workings necessary to seal the exploited mines increases in the world. As a result of experiments, technologies are developed that allow slurry to be pumped to fill free rock spaces or to liquidate rock mass discontinuities. The slurry preparation technologies can be divided into: subsurface and surface preparation and injection. Due to the pressure that forces the sealing slurry to move, the following can be distinguished: pressure technologies and technologies of gravity injection. The effectiveness of the work is determined by the correct selection of the technique and technology of the treatment and the selection of the optimal cement slurry recipe. The type of sealing liquid is especially important during works related to filling the exploited mine workings in salt mines. Therefore, this article presents the criteria for the selection of slurry recipes and their technological parameters, used for sealing and strengthening the salt rock mass. For this purpose, laboratory tests are carried out on various formulas of sealing slurries, prepared on the basis of full saturated brine and CEM I 32.5R Portland cement, ground granulated blast furnace slag, fly ash, and silt. The proposed concept for the selection of sealing slurry formulas has been positively verified during the performed works on sealing and strengthening the salt rock mass.

In order to ensure safe working conditions for miners underground, many works are carried out in mines to strengthen and seal mining excavations. This article presents the successfully applied technology for removing water inflow from the unique Salt Mine. Failure to take such action may ultimately lead to the flooding of the “Wieliczka” Salt Mine (KSW). On the basis of the authors’ research studies, some of the implemented works at the “Wieliczka” Salt Mine are presented, the purpose of which is to better protect the mine against the risk of flooding with water. Thanks to this, the mine can safely survive for many more years. This article presents two innovative technologies in salt mines: (1) sealing of the rock mass surrounding the Kościuszko shaft casing in the “Wieliczka” Salt Mine, where jet injection was used as the basic method of making an anti-filter screen outside the shaft casing and classic injection as a supplementary method for sealing the anthropogenic embankment; (2) reconstruction of the internal pillar of safety by implementing a patented technology called “pipeline injection” on the example of the Mina cross-section, in which a catastrophic water inflow was previously created that threatened the existence of the “Wieliczka” Salt Mine. The first method consists of making an anti-filter screen, which is located outside the shaft housing. Unfortunately, it is not possible to perform injection works from inside the shaft housing, because the Kosciuszko shaft, as a ventilation shaft, must be open constantly. To solve this problem, it is designed as the main technology known as jet grouting, which is supplemented by pressure injection at a depth of up to several meters with continuous monitoring of the condition of the casing during injection works. The second example concerns the reconstruction of the internal pillar of mine safety in the area of the northern border of the salt deposit. In this case, the catastrophic hazard is documented, as evidenced by the inflow to the Mina transverse, which is located on the fourth level of the mine. This task was successfully completed by the implementation of a patented technological solution called pipeline injection, the details of which are discussed in this article.

By creating a special edition entitled Fundamentals of Enhanced Oil Recovery, the editors focus on the problem of the global increase in energy demand

W celu obniżenia gęstości zaczynów przeznaczonych do uszczelniania kolumn rur okładzinowych w warunkach obniżonego ciśnienia złożowego czy w strefach skał słabo zwięzłych stosuje się lekkie dodatki, takie jak mikrosfera bądź perlit. Użycie tego rodzaju materiałów pozwala na zredukowanie wartości ciśnienia hydrostatycznego i tym samym zapobiega ucieczce cementu w strefy słabo zwięzłe. Dodatkowo zaczyny o obniżonej gęstości mogą być stosowane w przypadku konieczności tłoczenia cementu w przestrzeni pozarurowej na dużą wysokość. Jednak wykorzystanie dodatków redukujących gęstość zaczynu nie pozostaje bez znaczenia dla parametrów technologicznych zarówno świeżego, jak i stwardniałego zaczynu. W przypadku płynnego zaczynu obecność lekkich frakcji powoduje zmianę parametrów reologicznych zaczynu, wzrost wartości filtracji bądź też odstoju wody. Natomiast analizując parametry stwardniałego zaczynu cementowego, należy się spodziewać obniżenia wartości wytrzymałości na ściskanie, wytrzymałości na zginanie, przyczepności do rur stalowych itp. Z uwagi na konieczność stosowania w recepturach zaczynów lekkich dodatków redukujących gęstość w niniejszej publikacji omówiono to zagadnienie na podstawie przeprowadzonych prac badawczych. W artykule przedstawiono wyniki badań zaczynów zawierających 4 różne dodatki (mikrosferę glinokrzemianową dotychczas stosowaną, mikrosferę glinokrzemianową nowej generacji CSF K, mikrosferę szklaną oraz perlit filtracyjny E100F). Dodatki lekkie stosowano w ilości 15% w stosunku do masy cementu. Przeprowadzono badania dla zaczynu kontrolnego (bez dodatków lekkich). Zaczyn ten zawierał w swoim składzie środki niezbędne do kontrolowania parametrów decydujących o efektywności uszczelniania otworu wiertniczego. Następnie receptura kontrolna była modyfikowana dodatkiem lekkich frakcji. Przeprowadzono badania laboratoryjne parametrów technologicznych zarówno świeżych, jak i stwardniałych zaczynów cementowych. Na podstawie uzyskanych wyników określono wpływ badanych lekkich dodatków na parametry świeżych i stwardniałych zaczynów cementowych.

Fine-grained materials are used to seal the microstructure and improve the mechanical parameters of the formed cement sheath. They are used in cement slurries designed to seal casing columns at great depths and in geothermal boreholes to improve thermal conductivity. Such additions shorten the setting time and the transition time from the value of the initial time of the setting to the final of the setting. This allows the shortening of the time needed to bind the slurry and move on to further work. Additionally, it helps to eliminate the possibility of gaseous medium intrusion into the structure of the setting cement slurry. The goal of the work is to determine the influence of the Hblock fine-grained material on selected parameters of the cement slurry. Hblock is used in the research ranging from 1% to 20% (bwoc (bwoc—by weight of cement)), and the two types of cement most commonly used in the petroleum sector. Then the technological parameters of fresh and hardened cement slurries were tested. Research on rheological parameters, determined rheological models and flow curves are performed. On the basis of the obtained test results, the influence of the additive on the technological parameters of the cement slurry is discussed. The research results allow for further work and then the application of the fine-grained material in the petroleum sector.

In Poland, there are low-temperature geothermal reservoirs that can be used for various purposes in many regions of the country. Low-temperature deposits of geothermal waters are common and occur much more frequently than high-temperature deposits. They contain water with temperatures lower than 150 °C. Their temperature normally ranges from 20 to 90 °C. Achieving a state of equilibrium depends on many factors, including the kinetics of reactions between the individual components of the system, temperature, reactivity of reservoir rock, concentration of chemical components in the water and the time the water remains in contact with the rock. Therefore, this article presents the possibility of checking the conditions of precipitation of inorganic sediments in geothermal waters with the use of PVT equipment. Tests were carried out with the use of geothermal waters under given dynamic conditions (pressure, temperature and flow). This paper confirms the suitability of using the equipment for PVT (device for the study of phase changes) testing in order to determine the conditions for the precipitation of inorganic sediments in geothermal projects. Tests on the precipitation of solid sediments in geothermal waters were carried out. A result of the research is the adaptation of the equipment for PVT testing in order to determine the conditions for the precipitation of inorganic deposits in geothermal waters. As a result, different capillary blocking times were obtained depending on the measurement conditions (e.g., for P = 40 bar, T = 120 °C and q = 1 cm³/min, the blocking start time was 10.8 min). The authors found that solid sludge inhibitors, as well as other chemicals used, including paraffin inhibitors, must be periodically adjusted to prevent precipitation in geothermal waters.