Stick-slip oscillations are self-sustained and periodic twist and torque oscillations of a rotating drill string, characterized by large and harmful variations of the downhole rotation speed. This paper is a field evaluation of an active stick-slip prevention system.The evaluated system is active with smart control of the top drive, meaning the top drive speed is varied in a way that dampens stick-slip oscillations. It is software based, in many cases it requires no extra instrumentation and can be implemented on virtually any types and brands of top drives.The paper includes field test results, both from ordinary tests with surface data on top drive speed and torque, and from special tests including downhole measurements. The field data verified existence of the expected 2 nd mode stick-slip in longer strings and proved that the system is able to reduce the downhole speed variations. Therefore a general conclusion is that the active stick-slip prevention system significantly lowers the critical rotation speed below which stick-slip oscillations persist. Simultaneous surface and downhole measurements indicate that the reduction of stick-slip oscillations improved drilling performance and the rate of penetration (ROP).The positive field test results are good news to the drilling industry that has struggled for a long time with harmful stickslip oscillations, causing premature tool failures, excessive bit wear and poor drilling rate. Installation and use of an active stick-slip prevention system is therefore a very cost effective solution to a long outstanding problem.

Twenty-five wells in mature fields have been recompleted with a newly drilled horizontal leg. The experience has established a series of proven techniques for reopening, drilling, and recompletion. Additional oil recovery demonstrates economic viability of the system.

In today's high cost drilling environment, vibrations are recognized as the primary contributor to drilling inefficiency. As such, accurate prediction, identification, and quantification of vibration along the drill string has become increasingly important in order to reduce drilling costs. Near-bit measurements are also particularly important, as the drill bit is often predicted to be an important cause of vibration. This paper reviews a project within Ecuador, where high vibration and mechanical damage to drill bits has been observed, clearly affecting performance. This application is drilled with Fixed Cutter (FC) bits on a Rotary Steerable System (RSS) through a challenging sequence of formations including sandstone, shale, limestone, and conglomerates. Initial steps had been taken to optimize the drill bit design in terms of cutting structure, gauge geometry, and cutter technology. However, in order to truly understand the vibration issues, a unique downhole dynamic logging tool was utilized. This tool records drilling dynamics data at a high frequency sample rate, enabling lateral and torsional events to be accurately identified and recorded. Due to its size, and thus flexibility in string placement, the tool was located in two different points in the BHA.Evaluation and interpretation of the vibration data led to the recommendation of new drilling parameters, very different to traditional practices in this application, in a critical section for the next well in the same pad. This resulted from detection of torsional vibration, not only at the bit, but also at points along the BHA. Implementation of the recommended drilling parameters resulted in significant mitigation of torsional vibration at the bit and in the BHA. This resulted in reduction of wear to components within the BHA, as well as both time and cost savings in excess of $200K.

Drilling the Taoudenni Basin in Mauritania has posed a costly and time consuming challenge for operators looking to develop the basin economically. The formation's compressive strength limits the bit selection to heavyset PDC bits or hard rock roller cone insert bits due to their abrasive composition. One way to increase the effectiveness and drilling efficiency is to add a percussion force, increasing the axial energy, along with a hybrid PDC bit with PDC cutters and impregnated diamond material on the blades and secondary cutting structures.The main similarity between fixed cutter hybrid bits and roller cone bits is that both incorporate a similar means of energy transfer when used with a positive displacement motor. Axial weight from a drilling rig is applied while a hydraulic motor turns the bit at different speeds. A proposed improvement to this drilling system would be a new energy distribution system that induces axial oscillations and percussion force while still applying the same weight and torsional energy as previous systems.The system combines the torsional power of a conventional positive displacement motor with a high frequency axial pulse created by a mechanical action. The torque is still transferred directly to the bit and 100% of the hydraulic flow is utilized by the bit nozzles. The mechanical lifting and falling action creates a rapid variation in weight on bit (WOB), allowing the bit's depth of cut to fluctuate while overcoming different stresses. The percussion force created after each downward stroke, along with weight on bit variations, lead to increased rates of penetration (ROP).This system has already been utilized on two wells in Mauritania, drilling a variety of formations with PDC, hybrid fixed cutter and roller cone insert bits. This paper will focus on the 8½Љ interval, drilling the Atar Group and Jbeliat Teniagouri formations. These formations consist of sandstone, shale interbedded with siltstone, dolerite and pyrite. Confined compressive strengths range from 20 to 30kpsi in top section to 60kpsi in lower intervals where dolerite appears. This new technology increased ROP by more than 52% and interval drilled by over 100% through these intervals.

Carbonate formations in southern Mexico are commonly stimulated using matrix acidizing treatments to increase well productivity by removing near-wellbore (NWB) damage. Such damage can be attributed to accumulation of paraffin and asphaltene deposits during the productive life of the well and, in other scenarios, to fluid invasion while performing workover activities. A high perforation length across the reservoir to increase production from this highly natural-fractured carbonate has been the completion option for several years. The use of diverters is a common practice in the Bellota-Jujo field when multiple intervals are open. However, the effectiveness of the diversion had not been evaluated in real-time. A distributed temperature sensing (DTS) option was deployed to measure temperature profiles along coiled tubing (CT) equipped with an internal fiber-optic cable and a modular bottomhole assembly (BHA) consisting of pressure, temperature, and depth correlation sensors. This option was selected to monitor the treatment and help make real-time decisions. This real-time fiber-optic (RTFO) integrated system used during the stimulation allowed identification of zones with higher and lower admission. Based on this information, decisions were made during the pumping schedule, modifying volumes and rates of diverting agents and stimulation fluids being pumped through the annular space between production tubing and CT, also pumping through CT using a fluidic oscillating tool optimizing the diversion process during different stages of the intervention. This system enabled the operator to correlate depth and continuously monitor the temperature changes across the producing zone of the well. The findings and results of the stimulation treatment with this technique used in the well, Bricol 2DL, are presented in addition to the thermal analysis of the DTS profiles. The use of the RTFO integrated system during a matrix stimulation treatment in a carbonate formation with high permeability contributed to successfully evaluating the effectiveness of the fluids and mechanical diversion resulting in a well productivity increase of 60%, thus keeping the well in production since the treatment was performed.