scholarly journals Determining Fracture Pressure Gradients from Well Logs

2020 ◽  
Vol 8 (1) ◽  
pp. 5
Author(s):  
Udo K. I ◽  
George N. J ◽  
Akankpo A. O ◽  
Azuoko G. B ◽  
Aka M.U
Keyword(s):  
Niger Delta ◽  
Well Logs ◽  
Pressure Gradients ◽  
Seal Failure ◽  
Fracture Pressure ◽  
Shear Wave Velocities ◽  
Pore Pressures ◽  
Sonic Log ◽  
Drilling Operations ◽  
Sonic Logs

Fracture pressure gradient is one of the essential parameters used in determining mud weight profiles during drilling operations. We have determined fracture pressure gradients from well logs obtained from three producing wells in Onshore Niger Delta using an empirical model. Key logs needed for the prediction were conditioned and quality controlled to meet the standard required for reliable results. The true vertical stress, normal compaction trend and compressional shale velocity trends were generated from the logs (density and sonic logs). Poison’s ratio was obtained from compressional and shear wave velocities derived from sonic log. Pore pressures in the three wells were then predicted using Eaton’s Method. The predicted pore pressures, overburden pressures and poison’s ratio were used to determine fracture pressures using Ben Eaton’s Model. Results showed that there is a suitable drilling margin at all depths only in well G-005. Drilling well A-001 to a depth of 10962.81 ft and K-001 to a depth of 12626.9 ft will fracture the formations because the fluid pressures at those depths approximate the fracture pressures of 8536.7psi and 9506 psi with corresponding gradients of 0.78 psi/ft and 0.75 psi/ft respectively. The implication is that drilling deeper in the field will results in very low seal capacity magnitudes, thereby presenting a higher risk of top-seal failure.  

Determining Fracture Pressure Gradients From Well Logs

1973 ◽  
Vol 25 (11) ◽  
pp. 1259-1268 ◽  
Author(s):  
R.A. Anderson ◽  
D.S. Ingram ◽  
A.M. Zanier
Keyword(s):  
Well Logs ◽  
Pressure Gradients ◽  
Fracture Pressure

scholarly journals Prediction of Fracture Pressure in Niger Delta Deep Offshore

2021 ◽  
Vol 6 (2) ◽  
pp. 13-18
Author(s):  
Kehinde E. Ajayi ◽  
Azubuike H. Amadi ◽  
Victor D. Ola ◽  
Raphael E. Obonin ◽  
Nnaemeka Achara
Keyword(s):  
Niger Delta ◽  
Data Sets ◽  
Fracture Pressure ◽  
Maximum Value ◽  
Wellbore Pressure ◽  
Drilling Operations ◽  
Niger Delta Basin ◽  
Offshore Field ◽  
Window Design ◽  
Best Fit

During drilling operations, it is essential to keep the wellbore pressure within the maximum value of the fracture pressure and minimum value of the pore pressure of the formation. To handle this challenge, the fracture pressure of the formation must be known as it is significant to determining the mud window design. This study developed a correlation that could predict the formation fracture pressure in the Niger Delta deep offshore field. Two different fields were considered for this model named Field 1 and 2. From these fields, fracture pressure data were gotten from 21 wells during leak off test (LOT) at different casing shoe depths. While carrying-out the analysis of data, assumptions were made that the formations throughout the Niger Delta basin obeys the principle of horizontality. Also, that the fracture pressure at same depth is uniform with the pressure at other location in the Delta. Scatter plot was used as the tool for the data analysis. A line of best fit was drawn to arrive at the correlation. This correlation has an R2 coefficient values of 0.9969. In conclusion, the correlation gotten from this study for predicting fracture pressure has shown to align with some data sets from the Niger Delta fields with very little variation. This can be used for planning of further drilling operations in the Niger Delta to make it easier, faster and more economical.

Estimation of pulse shaping for well logs

Geophysics ◽  
2001 ◽  
Vol 66 (5) ◽  
pp. 1605-1611 ◽  
Author(s):  
K. Sølna
Keyword(s):  
Stochastic Model ◽  
Pulse Shaping ◽  
Well Logs ◽  
Well Log ◽  
Smoothing Effect ◽  
Sonic Log ◽  
Apparent Attenuation ◽  
Sonic Logs ◽  
Real Medium

A wavelet propagating in a finely layered lossless medium is subject to apparent attenuation that changes its shape. Can a sonic log be used to characterize this change? I show that numerical simulations with the well‐log as medium give an apparent attenuation or diffusion of the pulse that is very different from the attenuation in the real medium. This is due to the smoothing effect of the well‐log tool. Based on a version of the O’Doherty‐Anstey approximation, I derive an expression that reveals the role of the tool. Using a sonic log, I verify the theory and show how tool effects can be mitigated by deconvolution. I also propose a two‐scale stochastic model for the sonic log and a procedure for estimation of its parameters. One application of sonic logs is to quantify apparent attenuation and, in this context, my results are important.

Producing pore pressure profiles based on theoretical models in undrilled, deepwater frontier basins

2015 ◽  
Vol 3 (1) ◽  
pp. SE13-SE32 ◽  
Author(s):  
Sam Green ◽  
Stephen A. O’Connor ◽  
Deric E. L. Cameron ◽  
James E. Carter ◽  
William Goodman ◽  
...  
Keyword(s):  
Pore Pressure ◽  
Deep Water ◽  
Seismic Velocity ◽  
Theoretical Models ◽  
Seal Failure ◽  
Fracture Pressure ◽  
Pore Pressures ◽  
Pressure Profiles ◽  
Model Pore

A working petroleum system was established on the shelf in offshore Labrador with the Bjarni H-81 discovery in 1973 in the Hopedale Basin. The same reservoirs as those targeted on the shelf are present in the deep water, which is currently receiving attention as the result of newly acquired seismic data. To date, only a very small number of wells have been drilled in the deep water, i.e., Blue H-28, Orphan Basin, and none off mainland Labrador. The wells that were drilled in the deep water had encountered significant overpressure, e.g., kicks that indicated overpressures of 26,850 kPa in the Mid-Cretaceous. Therefore, it was reasonable to assume that pore pressures be similarly high for any new deepwater prospects identified. To help reduce the risk in unexplored environments, we developed an approach that can be adopted to model pore pressure in deepwater settings, with Labrador as the main case study area featured, but also we discussed other global examples such as the Vøring Basin, Mid-Norway. Our results indicated, as a first approximation, that seismic velocity-based pore pressures in shale-rich intervals were similar to the geologic model down to the Lower Tertiary. Deep lithologies were, by regional analogue, likely affected by cementation that will act to preserve overpressure generated by disequilibrium compaction by reducing permeability but will not generate additional pore pressure. The cements (and any carbonate or volcanic lithologies) will, however, result in faster shales and will underpredict pore pressure by mimicking low porosity. A theoretical or “geologic modeling” approach can be used to sense-check any pore pressure interpretation from seismic velocity. The geologic approach also can be used to assess the risk for mechanical seal failure by allowing for estimates of the pore pressure, and related fracture pressure, to be made without the effects of cementation that affect the logs and seismic velocity data.

Managing Wellbore Stability Window and Well Integrity by Adjusting the Tight Margin to Successfully Drill through Naturally Fractured Zone Onshore Niger Delta

2021 ◽  
Author(s):  
Bassey Akong ◽  
Samuel Orimoloye ◽  
Friday Otutu ◽  
Akinwale Ojo ◽  
Goodluck Mfonnom ◽  
...  
Keyword(s):  
Niger Delta ◽  
Wellbore Stability ◽  
Rock Properties ◽  
Failure Behavior ◽  
Natural Fractures ◽  
Gas Well ◽  
Well Integrity ◽  
Trajectory Formation ◽  
Naturally Fractured ◽  
Drilling Operations

Abstract The analysis of wellbore stability in gas wells is vital for effective drilling operations, especially in Brown fields and for modern drilling technologies. Tensile failure mode of Wellbore stability problems usually occur when drilling through hydrocarbon formations such as shale, unconsolidated sandstone, sand units, natural fractured formations and HPHT formations with narrow safety mud window. These problems can significantly affect drilling time, costs and the whole drilling operations. In the case of the candidate onshore gas well Niger Delta, there was severe lost circulation events and gas cut mud while drilling. However, there was need for a consistent adjustment of the tight drilling margin, flow, and mud rheology to allow for effective filter-cake formation around the penetrated natural fractures and traversed depleted intervals without jeopardizing the well integrity. Several assumptions were validly made for formations with voids or natural fractures, because the presence of these geological features influenced rock anisotropic properties, wellbore stress concentration and failure behavior with end point of partial – to-total loss circulation events. This was a complicated phenomenon, because the pre-drilled stress distribution simulation around the candidate wellbore was investigated to be affected by factors such as rock properties, far-field principal stresses, wellbore trajectory, formation pore pressure, reservoir and drilling fluids properties and time without much interest on traversing through voids or naturally fractured layers. This study reviews the major causes of the severe losses encountered, the adopted fractured permeability mid-line mudweight window mitigation process, stress caging strategies and other operational decisions adopted to further salvage and drill through the naturally fractured and depleted intervals, hence regaining the well integrity by reducing NPT and promoting well-early-time-production for the onshore gas well Niger Delta.

Surviving the Low Oil Price Cycle While Increasing Production Through Best Practices in Workover and Drilling Operations; Case Study of a Marginal Field in Niger Delta, Nigeria

2018 ◽  
Author(s):  
Longfellow Oghale Atakele ◽  
Osahon Noruwa Airhis ◽  
Ntietemi Ekpo Etim ◽  
Fisayo Jordan Ipoola ◽  
John Osadebe Anim ◽  
...  
Keyword(s):  
Best Practices ◽  
Niger Delta ◽  
Oil Price ◽  
Drilling Operations ◽  
Marginal Field

scholarly journals Integration of Well Logs and Seismic Data for Prospects Evaluation of an X Field, Onshore Niger Delta, Nigeria

2012 ◽  
Vol 03 (04) ◽  
pp. 872-877 ◽  
Author(s):  
Godwin Emujakporue ◽  
Cyril Nwankwo ◽  
Leonard Nwosu
Keyword(s):  
Seismic Data ◽  
Niger Delta ◽  
Well Logs

ROBUST SONIC LOG TRACKING USING A MULTI-RESOLUTION APPROACH

2021 ◽  
Author(s):  
Ting Lei ◽  
◽  
Michiko Hamada ◽  
Adam Donald ◽  
Takeshi Endo ◽  
...  
Keyword(s):  
Sudden Change ◽  
Processing Technique ◽  
Tracking Algorithm ◽  
Signal Loss ◽  
Tracking Accuracy ◽  
Signal Processing Technique ◽  
Waveform Data ◽  
Sonic Log ◽  
Tracking Process ◽  
Sonic Logs

Borehole acoustic logging is an acquisition method that is regarded as the most efficient and reliable method to measure subsurface rock elastic property. It plays an important role in both well construction and reservoir evaluation. The acquisition is carried out downhole by firing a transducer and then collecting waveforms at an array of receivers. A signal processing technique such as the slowness-time-coherence method is used to process array waveform data to resolve slownesses from different arrivals. To label these slowness values, a classification algorithm is then required to first determine if a primary (P) or a secondary (S) arrival exists or not, and then label out the existing ones at each depth of the entire logging interval to deliver continuous compressional and shear slowness logs. Such a process is referred as automatic sonic log tracking process. Clearly, it is of great importance to be able to track log as accurately as possible. Traditional approaches either use predefined slowness or arrival time boundary to distinguish them or treats slowness peaks in consecutive depths like “moving particles” and use a particle tracking algorithm to estimate their trace. However, such a tracking algorithm is often challenged by a sudden change in formation types at bed boundary, fine-scale heterogeneity, downhole logging noise, as well as unpredicted signal loss due to bad borehole shape or gas influx. Consequently, the tracking process is often a tricky task that requires heavy manual quality control and relabeling process, which poses significant bottleneck for a timely delivery of sonic logs for downstream petrophysical and geomechanical applications. In this paper, we propose a new physical based multi-resolution tracking algorithm that can improve the robustness of the tracking process. The new algorithm is inspired by the fact that different resolution sonic logs can sense different rock volumes and therefore response differently to a thin layer or an interval with bad borehole conditions. It works by grouping slowness-time peaks with different resolutions to form clusters, which are then tracked by the connecting with its neighboring depths. As different resolution slownesses are physically constrained by the convolution response of heterogeneous layers, the cluster-based multi-resolution tracking approach exhibits better logging depth continuity than the traditional single-resolution methods. Outliers due to noise can be confidently avoided. Finally, remaining gaps due to shoulder bed boundary can be patched by a convolution constrained optimization process from coherences from different resolutions. This new approach is therefore referred as a multi-resolution approach and can significantly improve sonic log tracking accuracy than the single resolution approach. This new algorithm has been tested on several sonic logging field data and demonstrates robust tracking performance of sonic P&S logs. Additionally, with the multi-resolution processing, sonic logs with different resolution can be reliably obtained and a high-quality high-resolution sonic log can also be automatically delivered, which can then be used to match resolution of other petrophysical logs for various types of interpretation.

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