**4. Possible causes of rapid production decline**

#### **4.1 Fracture network**

Fractures are lineaments that occur in rocks which represent minor breaks in the natural order of the properties of the rock [27, 28]. They are evidences of the brittle failure of the rock due to lithostatic stresses initiated by tectonism and other geodynamic processes [29]. Network of fractures and faults have been identified in the area (**Figures 12**–**14**). They appear as short, disconnected and network of dark patches around the well area on seismic time slices [25, 28].

Several factors may be responsible for the development of these fractures. These could be due to changes in lithostatic pressure, geothermal stresses, hydraulic pressure and high drilling density in the field [25]. There is presently no infill drilling opportunity on the structure due to high drilling activity. The regional stress somewhat affects the orientation of the fractures as some are parallel to the axis of the growth faults, whereas some have multiple orientations especially around the well area (**Figures 12** and **13**). Non-uniform fracture distribution and heterogeneity in natural fractured reservoirs (NFR) make the development of water-cut asymmetrical and estimation of critical rate and breakthrough time will require fracture pattern modeling for proper understanding of fracture development around the producing wells. Consequently, tectonics, geothermal processes and human activity (drilling, well stimulation) could contribute to fracture generation. Fracture patterns and high vertical permeabilities created are also two important flow parameters that will allow for rapid non-uniform flow of water into the well. The N5.2 sand

**21**

**Figure 14.**

**Figure 13.**

*Vertical fractures revealed in CT-scanned core sample p.*

*Geologic Characteristics and Production Response of the N5.2 Reservoir, Shallow Offshore Niger…*

falls between time slice 1346–1479 ms on the seismic section, where these fractures have been mapped, indicating that the reservoir is affected by the fractures. Five (5) CT-scanned core plugs taken from this interval also revealed the presence of massive vertical fractures (**Figure 14**) [25]. The vertical fractures radiate from the center of the core plugs to the edge, running around the internal circumference of

*Fractures highlighted to show orientations. Some of the fractures are aligned in the direction of the regional stress.*

*DOI: http://dx.doi.org/10.5772/intechopen.85517*

the core as concentric rings (**Figure 14**).

**Figure 12.** *Ant tracking at time-slice 1346.748 ms showing structural discontinuities.*

*Geologic Characteristics and Production Response of the N5.2 Reservoir, Shallow Offshore Niger… DOI: http://dx.doi.org/10.5772/intechopen.85517*

falls between time slice 1346–1479 ms on the seismic section, where these fractures have been mapped, indicating that the reservoir is affected by the fractures. Five (5) CT-scanned core plugs taken from this interval also revealed the presence of massive vertical fractures (**Figure 14**) [25]. The vertical fractures radiate from the center of the core plugs to the edge, running around the internal circumference of the core as concentric rings (**Figure 14**).

**Figure 13.** *Fractures highlighted to show orientations. Some of the fractures are aligned in the direction of the regional stress.*

**Figure 14.** *Vertical fractures revealed in CT-scanned core sample p.*

*Sedimentary Processes - Examples from Asia, Turkey and Nigeria*

**4. Possible causes of rapid production decline**

patches around the well area on seismic time slices [25, 28].

reservoir management decisions.

**4.1 Fracture network**

The hydraulic capacity of the sand-body was well understood from plots generated

from Winland and Rock Quality Index for flow zone characterization (**Figures 10** and **11**). Most of the samples plot within 1000 mD on Winland plot, showing a mega porous reservoir with a high quality index (**Figure 10**). Beside the presence of fractures that have created anisotropic condition in the homogenous geobody, excellent reservoir quality will enhance fluid flow in the reservoir [25]. Reservoir properties have major influence on reservoir fluids and the hydraulic behavior of the rock. It is important that these uncertainties are well understood because they are relevant to

Fractures are lineaments that occur in rocks which represent minor breaks in the natural order of the properties of the rock [27, 28]. They are evidences of the brittle failure of the rock due to lithostatic stresses initiated by tectonism and other geodynamic processes [29]. Network of fractures and faults have been identified in the area (**Figures 12**–**14**). They appear as short, disconnected and network of dark

Several factors may be responsible for the development of these fractures. These

could be due to changes in lithostatic pressure, geothermal stresses, hydraulic pressure and high drilling density in the field [25]. There is presently no infill drilling opportunity on the structure due to high drilling activity. The regional stress somewhat affects the orientation of the fractures as some are parallel to the axis of the growth faults, whereas some have multiple orientations especially around the well area (**Figures 12** and **13**). Non-uniform fracture distribution and heterogeneity in natural fractured reservoirs (NFR) make the development of water-cut asymmetrical and estimation of critical rate and breakthrough time will require fracture pattern modeling for proper understanding of fracture development around the producing wells. Consequently, tectonics, geothermal processes and human activity (drilling, well stimulation) could contribute to fracture generation. Fracture patterns and high vertical permeabilities created are also two important flow parameters that will allow for rapid non-uniform flow of water into the well. The N5.2 sand

**20**

**Figure 12.**

*Ant tracking at time-slice 1346.748 ms showing structural discontinuities.*
