Induced Fracture Modelling and Its Integration with Pressure Transient Analysis: Study for Shallow-water Offshore Field, South-East Asia – Part 1

Abstract

Numerous studies have been done on the design and analysis of hydraulic fractures. However, the study of induced fractures is still a maturing subject especially, with regards to the predictive capabilities of the fracture simulators and, it soon becomes a challenge when it comes to the acquisition of meaningful field data and their interpretations to validate the forward modelling results of the fracture simulators. The paper is a step forward to fill the gap between the model predictions and the field observations for water injectors in the context of induced fracture propagation. The study was done for a field, located offshore South-East Asia. The content of this study will be presented in two papers based on the key domains stated above – "field observations" and "model predictions". The current paper (Part 1) addresses the first subject where field data have been analyzed to get an understanding of the induced fracture growth in the water injectors. This comprises of "Pressure Transient Analysis (PTA)" of "Pressure Fall-Off (PFO)" tests done on the water injectors. The paper will present a workflow to interpret a PFO for fracture analysis using two approaches. The first approach is based on the standard PTA models where no explicit fracture mechanism has been invoked. We will introduce an analytical technique which uses the compliance value obtained from the standard model analysis to determine the fracture size. The second approach is based on the "Injection Fall-Off (IFO)" model, a dedicated Shell plug-in to Ecrin, used for fracture characterization. The workflow will be first illustrated elaborately through a stepwise interpretation of an example PFO test. We will demonstrate, afterwards, the application of the above methodology for analysis of a number of field tests using both approaches. The paper will conclude with a consistent picture of fracture growth interpreted from both techniques. Significance of geological set-up wrt the fracture growth will also be highlighted. We will also highlight some limitations with the modelling and ways around it.

Investigation on the pressure behavior of injectors influenced by waterflood-induced fractures: field cases in Huaqing reservoir, Changqing Oilfield, China

“…For Well D, the matched storage coefficient is 43.3 m 3 /MPa, which should not be wellbore storage coefficient only that presented in Case #3. Anand and Subrahmanyam [9] demonstrated that the fracture storage coefficient ) wellbore storage coefficient. Therefore, C f % 43.3 m 3 /MPa in this case, which is used to calculate fracture half-length as 73.5 m via equation (2).…”

“…In most cases, fracture storage coefficient is several orders of magnitude larger than wellbore storage [9]. Therefore, the wellbore storage coefficient can be ignored when calculating the fracture half-length by total storage coefficient.…”

“…These WIFs may be beneficial in improving injectivity or injection rates. However, if they are not managed adequately, it could be of great disadvantage (e.g., prematured water breakthrough in producers, steep rise in oilfield overall water-cut profiles, unpredictable flood pattern, poor sweep), which would lead to undesired oilfield performance [9]. Figure 2 shows an example in a certain oilfield.…”