The high costs associated with drilling operations, especially in offshore environments, make it necessary to optimize each step of the job. The drilling mud plays a critical role in the drilling operation, as it is responsible for several functions (solids transport, wellbore mechanical stability, signal sensor transmission, etc.). Besides that, the attention given to the control of drilling mud properties has not changed much from the last 50 years. Downhole and surface online measurements for several drilling parameters are available for anticipated diagnostics of operational problems. Drilling automation is already a reality (automated pipe handling, controlled tripping operations, etc.), but the drilling mud properties continues to be measured manually. The drilling mud sample has to be collected, transported, treated and analyzed to only then the measured property is reported. This work aims to present the development and result of experiments performed at a large scale drilling fluid loop, aiming the evaluation of commercial and built in property sensors. The following properties were determined: rheological parameters, mud weight, water-oil content, emulsion electrical stability (for oil based muds), fluid conductivity (for water based muds) and particle size distribution. The use of neural networks (Multi-Layer Perceptron type) allows the connection of the on-line equipment results to increase the reliability of mud properties determination. Comparisons with the results obtained from laboratory equipment were performed to train the neural networks as well validate the developed techniques.
Drilling operations in salt zones have gained importance in Brazil due to the discovery of large oil and gas reserves in the Pre-Salt area. Thus, the pursuit of excellence in such operations is requiring considerable development of new operational practices and technologies. Synthetic base mud has been the first choice to drill through evaporite sections in Pre-Salt zones. Synthetic fluids application practically eliminates salt dissolution and improves caliper quality. However, depending on the salt mobility rate, stuck bit and/or stuck pipe can happen, demanding the injection of fresh water pills for its liberation. In some wells, the frequent use of those pills resulted in enlarged sections. The situation gets worse in scenarios where loss of circulation is a major issue. On the other hand, the use of non-saturated aqueous fluids to drill soluble salts (e.g. halite, tachyhydrite and carnalite) can result in localized enlargements due to leaching process. Drilling a gauge hole is a very important issue to prevent wellbore collapse and/or problems in cementing operations. However, high operating costs associated to deep water drilling is placing additional emphasis on drilling performance in order to reduce the operational time, without losing the quality of the wells. This concern raises the issues of how to most effectively improve operational performance regarding the drilling fluid selection. The paper presents the results of the use of water based muds in the drilling of two offshore wells in Brazilian Pre-Salt area and highlights the lessons learned from the experience. Before the field application extensive lab tests and numerical simulations were carried out to support the drilling fluid design for the wells. In the first well, differences between the planned and encountered drilling conditions led to fluid replacement during the operation. On the other hand, in the second well, 2.000 m salt extension was successfully drilled to depth with no major operational problems and good drilling performance. The field application of WBM proved to be a good option to drill the salt layers in the development of Pre-Salt fields but it demands a more detailed knowledge of both lithology and stratigraphy of the evaporite section. Introduction The drilling fluid design for salt zones uses to focus on drilling a gauge hole to prevent wellbore collapse. Due to solubility issues, synthetic based emulsions have been selected as the first option to drill through evaporite layers in the Pre-Salt scenario. However, high operational costs associated to deep water drilling have brought special attention to drilling rates in order to reduce operational time without loss of well quality. In offshore drilling operations, the use of synthetic based drilling fluids demands the use of centrifuges to clean the cuttings before they are discharged into the sea. This procedure results in strict control of penetration rates due to cuttings processing issues. Moreover, in scenarios where lost circulation is a major issue the use of synthetic base muds may not be the best choice. Therefore, the challenge is to find the best way of effectively improving operational performance through an adequate drilling fluid selection. And it raises the question: should water base mud (WBM) or synthetic base mud (SBM) be used? In Brazilian Pre-Salt scenario, the most common salts encountered are halite (NaCl), carnalite (KCl. MgCl2.6H2O), tachyhydrite (CaCl2.2MgCl2.12H2O) and anhydrite (CaSO4). The deposition sequence normally is the opposite of the salt solubility in water which, for these salts, follows the same sequence of easiness of reaction with water: Tachyhydrite > Carnalite > Halite > Anhydrite. So, they might dictate some formulation choices to avoid dissolutions. In that aspect, the synthetic fluid is preferred over water based muds, because it neither has free water nor interferes in the crossed salts solubility. The well caliper tends to be in gauge when compared with the saturated water base fluid.
-Drilling an oil well involves using drilling fluids that perform cleaning and cooling functions, but that most importantly maintain the fluids of the geological formation contained by hydraulic pressure. A fundamental role in predicting the hydraulic pressure of the well consists of monitoring the fluid's rheological behavior. This paper summarizes an ongoing effort to measure, by evaluating the performance of two online viscometers, drilling fluids' rheological behavior in real time. One online method proposes a modified Couette system. The other consists of a standard pipe viscometer with default modeling. The performances of the online devices were compared with an offline method -a Couette device commonly used in oilfields as a benchmark. For Newtonian fluids, agreement between the rheological behaviors was found for all instruments, validating the methodology proposed. For non-Newtonian fluids, there were divergences, which were investigated and their probable causes determined to be the following: homogeneity, slippage effects, and interaction in the fluid/gap interfaces. A case study demonstrated that these divergences were not significant during the prediction of hydraulic pressure, meaning that the methodology proposed has the potential to improve overall drilling performance.
This article summarizes efforts conducted by PETROBRAS and partners aiming offshore oilwell drilling automation. The first step includes the implementation of a drilling problem detection software which operates with online real-time data analysis. The second step includes the concept of an integrated model to represent the process of drilling and the third an experimental pilot scale facility constructed to test control algorithms for MPD and influx control operations.
Well construction is a complex job in which annular pressures must be kept inside the operational window (limited by fracture and pore pressure). Monitoring bottomhole pressure to avoid fluctuations out of operational window limits is an extremely important job, in order to guarantee safe conditions during drilling job. Several operational parameters have a direct impact on bottomhole pressure such as flow rate, rate of penetration, drilling fluid properties, etc. This way, due to the several parameters to be handled, bottomhole pressure control is a complex task and is (nowadays) a manual and very subjective job. Thus, control and automation of drilling operations is a required activity for future challenge of petroleum engineering. This job presents the results of the implementation of a phenomenological model aiming the development of a classic PI (proportional - Integral) controller for bottomhole pressure during a drilling job. Some strategies were investigated by handling flow rate and a choke opening. An experimental unit was built to study pressure control, when the system is disturbed by an ROP steps or choke openings. Results show a non linear behavior, what requires the system investigation in different operational conditions in order to make a classic PI controller reliable. This fundamental study represents an important step in the understanding the requirements for the implementation of the drilling automation process.
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