The high structural uncertainty present in a field in Egypt required special logging-while-drilling (LWD) measurement specifications to achieve economically satisfying production results. East Zeit Oil Company (Zeitco) was targeting an oilbearing sandstone reservoir that is characterized by the presence of subseismic faults and high structural uncertainty. This uncertainty ranges from 6° to 23° in structure dip, which makes drilling successful horizontal wells in this reservoir challenging. A well with a horizontal penetration envelope from a minimum 500 ft measured depth (MD) to an optimum 1,600 ft MD was planned for this reservoir to make the well economic. Steering in such a challenging reservoir required having realtime measurements as close as possible to the bit to make the required real-time decisions. A real-time density image and with other azimuthal data were the primary measurements used in steering this horizontal well. Being used with a rotary steerable tool, the multifunction LWD tool provided density image at only 39 ft behind the bit, which was crucial for the success of the well. The well was successfully drilled with 100% exposure inside the sandstone reservoir with 1,532 ft MD horizontal penetration. In addition, well testing results indicated a natural flow of 2,000 BOPD, which made this well the highest oil producer in the field.
As part of any successful development plan of any hydrocarbon field, drilling boreholes safely is a key factor to make the entire process safe, economic and environmentally friendly. One of the main factors that dictates whether a borehole is going to be drilled safely or not is to understand the geomichanical behavior of the different formation to be penetrated. A definition of geomechanics could be stated as the science that studies the relationship between each of; in-situ stresses, rock mechanics, and the drilling fluid properties. In Kuwait and during the course of efforts to develop Wara channel sands in Minagish Field to the west of the country, Kuwait Oil Company (KOC) realized that continuing to drill development wells using conventional drilling practices is not any more an easy task. Considerable non-productive time has been recorded due encountering events such as shale carvings and pack off leading to stuck pipe. In addition, partial to total lost circulation were faced while drilling through Mutriba Formation which added to the complexity of problem. This study involved gathering data from offset wells to build a mechanical earth model for the area where the new well is going to be drilled. The main objective of having the model built is to perform wellbore stability analysis (WBS) and compute the quantitative mud window values to insure stable and safe borehole drilling. As the case of any study, performing reliable WBS analysis requires accurate modeling of earth stresses and rock mechanical properties. This process is primarily based on sonic logs (compressional and shear slowness), formation bulk density and lithology distribution. The study started with an audit of the available data sets in the region to select the best offset wells and generating empirical correlations to fill- up any missing and/or poor-quality data zones. Initially,7offset wells were identified, based on the geological distribution and data availability.Out of them, only four wells were found to have compressional slowness and three with bulk density measurements. However, it is worth mentioning that no shear slowness measurements were available in any of the offset wells in the region. Due to this, a correlation based compressional-shear relationship from nearby wells was proposed for the pre-drill study. The mechanical properties were characterized using the tri-axial core test results available from Wara and Burgan Formations. Empirical correlations were developed to obtain static mechanical properties from the dynamical mechanical ones and log responses. In addition, horizontal stresses in the region were constrained with formation integrity test data to have better control on the model. Finally, after the WBS model was built,it was compared to the available caliper data from the offset wells for calibration purposes. The resulted pre-drill geomechanics model was used to advise on the drilling parameters (mud weight) to be used in drilling the new development well. Moreover, and being the first realtime drilling geomechanics (RTDG) job in in Kuwait, an LWD sonic was used while drilling to supply the pre-drill model with realtime compressional and shear slowness measurements. Having the model updated in realtime with data from the formation at the borehole location resulted in optimizing the mud weight window limits by the geomechanics engineers as the well was being drilled. Following these mud weight recommendations based on the updated pre-drill model resulted in a smooth landing and horizontal sections in which all the wiper trips until the final pull out of hole were smooth.
The Cenomanian Wara Formation in Minagish Field is composed mainly of coastal plain deposits, observed at field scale along with shallow marine shales and carbonate bioclastic sandy beds. They are locally disrupted by embedded channelized sandy bodies from fluvio-tidal origin. The reservoir units are represented by different channel geometries with limited areal extension. The placement and completion of horizontal and highly deviated wells in such reservoir is a challenge necessitating a collaborative approach to avoid major well bore instability issues. These issues have a significant impact on the well cost and time line. In addition, having the right placement and completion is important for optimizing the drainage contact. To address such challenges during the different stages of the drilling operation, different technologies were used. For example, while the well was drilling through the unstable Wara and Ahmadi shaley formations, a Logging While Drilling (LWD) sonic and gamma ray (GR) tools were used to update in realtime a predrill geomechanical model with the formation acoustic and GR properties. Having such measurements allowed calculating the right mud weight density which resulted in drilling a stable borehole. This was confirmed by the absence of cavings and tight spots thought out the whole operation. On the other hand, the drain section was drilled in Wara channel sands which are known to be composed of a thinly bedded faulted sand-silt sequence with the sand layers being relatively radioactive. To help steering in such complex environment, a combination of LWD tools were chosen to place the well in the sweet spot of the target. These tools involved using the advanced deep azimuthal resistivity (geosteering) and the Multi-Function LWD (advanced petrophysics) tools. As a result of this, the horizontal section was proactively geosteered in the reservoir in which 1049 ft MD were steered in the high-quality sand layers.
Umm Ghudair Field is one of the major oil producing fields in West Kuwait. Oil was discovered in 1962 in the Lower Cretaceous Minagish Oolite Formation and more than 200 wells have been drilled to exploit this reservoir since then. Stratigraphically, the formation is defined by three units; Lower, Middle and Upper. The lower and upper units are considered non-reservoirs, while the middle one is hydrocarbon bearing. However, because of the continuous production over the past 50 years, the filed started to show a variable rise in its oil water contact (OWC). Consequently, this uncertain OWC rise has impacted the planning and production of the newly drilled wells (deviated and horizontal). Several recently drilled wells showed water breakthrough much earlier than expected. To address this challenge and with an attempt to proactively predict the current OWC depth in the new wells to be drilled, Kuwait Oil Company (KOC) decided to try the new High Definition Reservoir-Mapping-While-Drilling (HD-RMWD) technology in one of the horizontal well in their field. The objective was to assess the potential of the technology in detecting and mapping the current OWC while landing the well in the target. Due to the ultra-deep detection range of the technology (in excess of 200 ft), the landing point could be adjusted proactively and early enough to accommodate any unexpected OWC depth changes in the field.
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