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To prevent the degradation of the borehole and also the disintegration and dispersion of drilled cuttings, different shale stabilizing additives are used in water-based drilling fluids (WBFs). Glycols, poly(ethylene glycol), glycerols, and polyglycerol derivatives, also called polyols, have been used to inhibit shales containing reactive clays in WBF. These additives are normally used in conjunction with KCl to reduce clay swelling and dispersion of drilled cuttings. Highly branched polymers have become an important field in current polymer science. Such materials typically exhibit compact, globular structures in combination with an exceptionally high number of sites with functional groups. They have unique properties that differ significantly from their linear counterparts, and the hyperbranched polyglycerol (hPG) is an important hyperbranched polymer that can be produced from an environmentally benign monomer, the glycerol carbonate. In this article, the clay inhibitive properties of hPG were evaluated by different test methods including bentonite inhibition test, cuttings recovery, and X-ray diffraction measurements. The results show that the hPG has a great potential to be used as an environmental friendly inhibitor additive in WBFs.

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.

The anticipation and remediation of operational problems while drilling an oilwell is the main goal of real time measurements of drilling parameters, such as bottomhole pressure, flow rate, pump pressure, torque, drag, among others. The petroleum industry has spent a great amount of financial resources to ensure the quality and availability of these data, but the knowledge for a correct analysis and interpretation of them is still far from being spread among the rigsite teams and drilling engineers. Nowadays, the interpretation of real time drilling data to identify possible operational problems is done by a drilling analysis specialist. However, this can be a very subjective job since it depends on the specialist experience. These analists also take their decisions based on intuition and qualitative rather than quantitative criteria. Petrobras has developed a computational tool (called PWDa) to interpret real time drilling data, predicting and analyzing drilling operational parameters (such as pump pressure, bottomhole pressure, torque and drag). The software detects abnormal behaviors (such as an unexpected increasing trend on bottomhole pressure) and establishes quantitative criteria in order to identify a possible cause, suggesting corrective and/or preventive actions. The main goal of the software is the establishment of an automated methodology to interpret operational parameters in real time helping the drilling engineers to take right and fast decisions. The software is being currently implemented at Petrobras Real Time Operations (RTO) rooms and is providing good results. Over 70 wells have already been monitored with PWDa and several operational problems (such as washout, mud losses, bit wear, downhole motor fail, deficient hole cleaning, pore pressure increments, etc) were successfully identified, allowing the operators to take fast decisions and avoiding riskier situations. The wells monitored include deep water exploratory wells (mostly), directional development wells and extended reach wells. This work aims to highlight the benefits generated by the implementation of the technology. The interaction with the drilling team, including operator and service company members will be discussed. Introduction The analyzis of PWD (Pressure While Drilling) data and other operational parameters (such as rate of penetration, standpipe pressure, flow rate, torque, drag, etc) is an important tool to identify and prevent several operational problems (Aragao et al). The real time interpretation of these data may be very useful to reduce non productive time, risks and operational costs. According to Teixeira et al, most of events and problems have direct or indirect impact on bottomhole pressure and standpipe pressure. Some of them may also affect torque and drag. Problems like poor hole cleaning, annular obstructions, wellbore collapse, kicks, washouts and mud losses will affect the amount of solids in the annular space and/or friction losses and, therefor, will directly affect standpipe and bottomhole pressure (Aragao, et al, 2005). Thus, the analysis of pressure data is a key element to identify and prevent operational problems. Additionaly, when other parameters are simultaneously analyzed (modlogging measurements, for instance), the interpretation becomes much richer.

This article details the field implementation experience of an in house developed system for drilling problems detection and identification. Starting from real time drilling data (including MWD, PWD and mud logging sources), the system was designed to investigate reasons for deviations in important measured variables (such as downhole and pumping pressures, temperatures, torque and drag, etc.) during drilling operations. Based on a hybrid approach, including multi phase hydraulics and torque & drag modeling, case history matching and specialists knowledge, the system should identify undesirable events, such as influxes, poor solids transport, bit balling, bit wear, drillpipe washouts, hole instabilities among several others.Field implementation issues includes offshore installations and remote operations from onshore decision support rooms, necessity of team working, requirements for conventional and MPD operations, software calibration and validation challenges and continuous knowledge updating. Examples highlight the benefits on investing in data interpretation and drilling automation technologies for deepwater exploratory scenarios.