Naveed, Muhammad (Schlumberger) | Kirthi Singam, Chandrasekhar (Schlumberger) | Viandante, Mauro (Schlumberger) | Ali Malik, Kashif (Schlumberger) | AKhmadeev, Vadim (Schlumberger) | Jury, Ben (Woodside Energy) | Belson, Will (Quadrant Energy) | Wroth, Andy (Vermilion Oil and Gas Australia)
It is widely recognized in the industry that 30m survey intervals are too large to capture the true trajectory of the directional borehole and can result in significant True Vertical Depth (TVD) errors. This is particularly true when drilling with motors or geosteering in reservoirs with tight-TVD tolerance. Based on experience with horizontal wells drilled in North West Shelf (Vincent, Wandoo and Coniston drilling campaigns), a new technique of high definition surveying (HDS) was introduced.
The North West Shelf (NWS) in Australia imposes significant challenges for maintaining constant directional control while drilling in sand layers, which can be unconsolidated and include or traverse faulted or fractured zones. In such formations, TVD control in horizontal wells is a challenge. To improve control, extra surveys would be needed to reduce the vertical uncertainty; this process would be very time-consuming iand adds a risk of stuck pipe and hole washout.
Additionally, as the field become more congested through infill drilling, the risk of collision with nearby wells would increase because of poor TVD control.
The HDS gives a more accurate reconstruction of the wellbore position while drilling with respect to the pre-drilled geological model all the way out to target depth.
Reservoir mapping while drilling (RMWD) and Bed boundary mapping (BBM) services both measure the distance to nearby boundaries. These services map the form and position of reservoir boundary structure with respect to the associated well path. Therefore, the position of the reservoir structure in space is directly related to the directional wellbore survey. An inaccurate survey leads to errors in reservoir geometries and structural tie-in to the adjacent exploration and development wells. Because the wellbore is more accurately defined using HDS, so is the reservoir structure when coupled with RMWD services. This greater definition has enabled better well planning to drive maximum value extraction from reservoirs. With these features in place HDS has become an integral part for RMWD and BBM Services.
This paper illustrates the potential benefits of using HDS as a further service quality improvement component applicable to drilling horizontal wellbores and gives examples of practical implementation such as borehole tortuosity, torque and drag modelling, well placement and drilling and completion optimization.
Dong, Cindy (Schlumberger) | Dupuis, Christophe (Schlumberger) | Morriss, Chris (Schlumberger) | Legendre, Emmanuel (Schlumberger) | Mirto, Ettore (Schlumberger) | Kutiev, Georgi (Schlumberger) | Denichou, Jean-Michel (Schlumberger) | Viandante, Mauro (Schlumberger) | Seydoux, Jean (Schlumberger) | Bennett, Nicholas (Schlumberger) | Zhu, Qingfeng (Schlumberger) | Zhong, Xiaoyan (Schlumberger)
The data delivered by a new reservoir mapping while drilling (RMWD) tool provides more geological information than that from any other logging-while-drilling (LWD) technology previously available in the oil field. Its answer product images the surrounding formation structure, and the resulting maps can be used by the geoscientists to improve their understanding of the subsurface, the well placement and the reservoir.
To take advantage of the richness of the measurements and deep depth of investigation across multiple formation boundaries, an automatic stochastic inversion has been developed that combines approximately a hundred phase and attenuation measurements at various frequencies and transmitter-to-receiver distances. This efficient Bayesian model-based stochastic inversion runs in parallel with multiple independent search instances that randomly sample hundreds of thousands of formation models using a Markov chain Monte Carlo method. All samples above a quality threshold over the solution space are used to generate the distribution of formation models that intrinsically contain the information for model uncertainties.
RMWD is a highly nonlinear problem; inverting for a unique solution is analytically difficult due to the well-known local minima issue. The stochastic method addresses that by sampling thousands of possible formation models and outputting a distribution of layered models that are consistent with the measurements. Statistical distributions are displayed for formation resistivity, anisotropy and dip at each logging point. Additionally, the median formation models for resistivity are shown along the well trajectory as a curtain section plot. This provides an intuitive interpretation for the entire reservoir formation around the tool. The inversion curtain section plot can be overlaid with the seismic formation model for combined interpretation. Furthermore, the curtain plot provides graphical information for dip and distance to boundary, which are critical for field applications such as landing, geosteering, remote fluid contact identification, etc. The stochastic-sampling-based answer product has been intensively field tested and has proven to provide reliable estimation of the formation geometries and fluid distributions in many locations and geological environments worldwide.
Field applications and simulated examples of the stochastic inversion include remote detection of the reservoir to enable accurate landing, navigating multilayered reservoirs, remote identification of fluid contacts and reservoir characterization in the presence of faults.
The stochastic inversion samples the formation properties randomly and provides the distribution of formation properties based on a large number of samples, instead of providing only the most likely solution as is typical for deterministic inversions. A statistical method of presenting inversion results in formation space provides an instant and intuitive understanding of the formation surrounding the tool. Quantifying the non-uniqueness of the inverted formation models gives geologists a more robust insight into what the formation scenarios may be, and helps with the steering decision-making and reservoir mapping interpretation.
A development campaign offshore Australia, with a total of 15 laterals in a challenging geological environment, has been successfully completed by Quadrant Energy. The main objectives were to geosteer and place the well path at an optimum standoff from the oil/water contact (OWC), while drilling at the interface of the gas/oil contact (GOC), when present, and at 1-1.5m TVD from the reservoir top when not.
The field is characterized by a series of transverse and longitudinal seismic and sub-seismic faults that bisect hydrocarbon-bearing sands which represent the greatest challenges in this development campaign. Evidence from exploration wells showed a thin column of heavy oil and a gas cap in the fault-bonded reservoir. A new multi-disciplinary methodology not only enabled Quadrant Energy to achieve its development objectives, but to develop a full subsurface picture of the Coniston field reservoir.
The use of the Reservoir Mapping-While-Drilling (RMWD) combined with Bed Boundary Mapping Tool (BBMT) and Multi-Function LWD services enabled the laterals to be placed at 1-2m TVD below the reservoir top or gas cap, when present, even in highly faulted sections. In addition to this precise placement the extreme depth of investigation of the RMWD service, in conjunction with the real-time multilayer inversion capability, constantly mapped the OWC at a distance up to 19m TVD below the wellbore. While drilling, different qualities of reservoir sands were identified and enabled the extensions of the wells’ TDs based on reservoir properties. The distance to boundary information, provided in real-time by the RMWD service, was used in real-time by the Quadrant Energy geology and geophysics team to update and validate the seismic model that provided increased confidence in the reservoir model and a more precise planning for future development wells.
This paper will illustrate the use of the latest LWD RMWD technology in a challenging geological environment. The paper will explore the close collaboration, teamwork, and integration necessary to drive innovation and demonstrate the outcomes of this successful campaign which have not only exceeded the development goals, but have also generated a full 3D view of the reservoir.