APIT is a computational software based system which performs real-time test analysis, reporting and automated result interpretation of FITs/LOTs/XLOTs based on surface and downhole data. This paper presents the challenges for the current pressure integrity testing and introduced a new solution called automated pressure testing (APIT) system. This has included system framework and integration to cementing units, models and algorithms to determine system compliance and fluid leakage, fracture closure pressure, calibration techniques and validated results. Based on a minimum of preconfigured user input, the APIT system covers all test phases, from pressurization, fracture propagation to shut-in and flowback. The system identifies unexpected test behavior and triggers warnings by continuously evaluating key test metrics such as leakage rate, system compliance and surface pressure during each test phase. This APIT system was tested optimized and validated using various historical field data in order to provide Proof-of-Concept of algorithms, test sequences and graphics user interface (GUI). Both successful and unsuccessful data chosen from NCS and the international arena were tested. The automatic interpretation algorithms from APIT are aligned with manual test interpretation performed internally in Statoil. The APIT system is believed to be a safer and more efficient pressure testing alternative to the current manual counterpart.
Fluctuations in the returned mud volume have often been observed when drilling HPHT wells. There are several contributing factors for this, out of which increased wellbore volume due to elastic deformation and mud taken by natural fractures are considered in this paper. These effects are significant in HPHT wells as a result of the high mud pressure required to control the well. This, however, can give the driller the misimpression that the extra mud volume is lost to the formation due to wellbore breakout and/or fractures. When the mud weight is reduced to prevent such a suspected mud loss, the formation quickly regains its original volume and the "lost" mud is returned. This might again be misunderstood as a kick and the mud weight is increased immediately to prevent the suspected kick. The repetition of this process a few times might eventually lead to an actual wellbore failure. This paper presents a method to estimate the volumetric expansion of wellbores as a function of wellbore pressure. The wellbore near-breakout/fracture pressure, which is of interest for this analysis, is established by considering different failure modes including helical shear, elongated shear and tensile fracture. The increases in wellbore volume are estimated at this pressure as a limit below which the driller should not be fooled by the suspected breakout/kick situation and thus avoid it leading to wellbore failure. The method to estimate the volumetric expansion is based on analytical and numerical approaches. Analyses show that the diametric expansion of the wellbore may be in the range of centimetres at a critical pressure, and thus a deep well may consume a significant number of extra mud barrels before actual breakout occurs. This might be alarming enough to lead the driller to suspect breakout/fracturing in the absence of any analytical guidance. Thus, the paper has presented a novel approach to analyse such a suspected situation during well drilling at HPHT conditions, and the information presented will assist engineers to avoid confusion and manage the well efficiently in such a situation. Introduction Volumetric changes, both positive and negative, in the mud system during drilling operation is commonly termed ballooning. The change in volume, or ballooning volume, can be quite large depending on the well in question, and might as such give a false impression on the surface that the well is either taking a kick or that there is a lost circulation scenario. To address this problem, especially in High Pressure High Temperature (HPHT) wells where the safety margins are often quite small, various studies have been conducted in the past to be able to quantify the ballooning volume. It is commonly accepted that the potential causes for ballooning is mud expansion or contraction due to both temperature and pressure variations, deformation of borehole and casing and loss of mud to natural fractures. Bj rkevoll et al1 and Aadnøy2, based on the same two example wells, conducted a study into the effects of both mud expansion and contraction and the deformation of both borehole and casing by both numerical and analytical means. From these studies it was concluded that the mud ballooning was by far the most significant effect, with only minor contribution coming from the deformation of borehole and casing. Further works on the subject of mud ballooning were carried out by Kårstad and Aadnøy3–9. However, the method used in these works to calculate the effects of elastic deformation is based on the change in well pressure, without any consideration of in-situ stresses. In addition they were considering fairly hard formation types, with E moduli of 30 GPa and 10 GPa. Combining this with open hole radii of 12.25" and 8.5" respectively, the total deformed volume is small, whereas, using the same input data, the method proposed in this paper estimates a higher deformed volume.
A fit for purpose 4D Geomechanical model is regarded valuable for most fields. Although tools for building such models have been available for some time they are commonly not made or not fully utilized due to the extensive amount of time, complexity and costs involved. In Equinor a workflow (DE4RM) has been developed for fast 4D geomechanical modeling, effective visualization and interpretation. Using this workflow, models have been built for more than 20 fields over the last 4 years and results applied for a variety of areas including input to seismic time shift analysis, short and long term well planning, estimation of cooling effects from injectors, subsidence/compaction predictions, input to well completion, monitoring optimization, overburden integrity studies, out of zone injection and fault re-activation assessment. Some examples on such use will be given in this paper. On the modeling side key factors for efficient modeling are utilization of existing reservoir models, use of commercial finite element software and a streamlined, easy to use, workflow for all pre-processing steps. Particularly, a well-equipped toolbox for various grid-editing functionality has been essential for being able to complete the modeling fast enough (1-3 weeks). Once a model is built it is readily available for both geomechanical experts and non-specialists through the open source powerful visualization platform Resinsight. In this software geomechanical capabilities have been developed over the last years guided by practical use of the models. Further development on both the modeling, visualization and post-processing side is ongoing and as Resinsight is open source, use of the software and development of new functionality is possible for anyone. In summary, 4D geomechanical modeling and utilization of such models has become a daily activity in Equinor for numerous applications, gradually replacing simplified 1-D based methods with the faster and more accurate DE4RM methodology.
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