Thomas Kruspe

Active cooling of downhole instrumentation for drilling in deep geothermal reservoirs

To ensure efficient geothermal energy exploitation, hot and deep reservoirs have to be drilled. During the drilling process all components of a downhole drilling and evaluation system, which can be a measurement while drilling (MWD) or a wireline tool, are exposed to harsh environmental conditions like strong vibrations and temperatures up to 250°C. These high temperatures can impact the electronics or sensors of the bottom hole assembly. Therefore, for deep and hot geothermal wellbores, active cooling provides an option to extend the life time of the components and improve the reliability of the entire system. Techniques that lower the temperature inside the cooling system below the downhole temperature that exists in the wellbore are considered as active cooling methods. Thermal insulation is critical for the efficiency of an active cooling system. Phase change from solid to liquid as well as from liquid to gas provide a good compromise between cooling power, cooling time and independence from electrical power. Several active cooling methods were investigated. An example of a phase change from liquid to gas in combination with a sorption process is explained in more detail and in combination with experimental results.

Collaborative Development of a Slim LWD NMR Tool: From Concept to Field Testing

ABSTRACT Nuclear Magnetic Resonance (NMR) was identified as a critical technology for reducing uncertainty and minimizing risk during the planning phase of a major field development project. The reservoirs in the subject field contain heavy oil/tar in the flanks, a nd accurate knowledge of viscosity trends becomes essential for the placement of water injectors. Since NMR logs can be used to estimate heavy oil viscosity, the development plan required running logging while drilling (LWD) NMR logs in the extended -reach horizontal injectors, in addition to some selected producers. A program heavily based on slim hole drilling presented a practical challenge for the execution of the development plan, since at the time no service company offered slim hole LWD NMR services. Considering the business impact of this technology gap, Saudi Aramco decided to collaborate with the service industry to develop LWD NMR technology for hole sizes ranging from 5⅞ ” to 6⅛”. Within a year, a joint project was established with a major technology provider for the development of a slim LWD NMR tool. The fi rst two prototypes were delivered for field testing in less than 18 months. The prototypes have been run in nearly a dozen wells to date and in a variety of environments, including extended-reach wells with high salinity muds. Data obtained from drilling and reaming runs agree very well with those from other porosity tools, including wireline NMR. Furthermore, close coordination and cooperation between the operator and the service provider during testing runs have resulted in significant improvements in downhole firmware, data acquisition modes and signal processing. Two factors weigh heavily for the successful fast delivery of the project goals: clear requirements from the operator, and proven expertise in NMR tool design from the technology provider. Giv en continuing reliable and robust performance from the prototypes, the slim LWD NMR service is expected to be commercially available shortly. In fact, the high level of confidence gained from early field tests has already allowed the use of the data in cri tical well placement decisions in some wells.

Sinter-attach of Peltier dice for cooling of deep-drilling electronics

We evaluate Ag particle sintering as a highly reliable die attach technology for the assembly of thermoelectric modules. Bismuth telluride (Bi2Te3)-based Peltier coolers are realized using Ag sintering and tested for high-temperature applications (e.g. Measurement-While-Drilling, MWD). Bonding takes place at a pressure of 6 N/mm2 and a temperature of 250°C for 2 min. Shear tests are performed for evaluating the adhesion according the American military standard for chip-substrate contacts (MIL-STD- 883H, method 2019.8). Sintered layers are analyzed for porosity, Youngs modulus, electrical conductivity, and thermal conductivity. It is shown that due to specific additives (i.e. micro-diamond particles) the coefficient of thermal expansion (CTE) of sintered Ag layers can be reduced to meet the requirements of Bi2Te3 as well as next-generation thermoelectric materials (e.g. skutterudites) for minimized thermally induced stress during drilling.