Prediction of Fracture Extension During Waterflood Operations

Abstract

ABSTRACT A fracture extension mechanism was proposed to explain daily surface injection pressure behavior observed in a waterflood project located in the Somatito Field A fault block in the Talara Area of Northwest Peru. Daily surface injection pressure data indicated a repeating phenomenon, i.e., formation pressure increasing slowly along a general trend as the flood continued (called normal formation recharge). Surface injection pressure occasionally built up above this trend value because of fracture plugging. Then the injection pressure dropped back sharply to the general trend (called fracture extension). The mechanism repeats again and again in the same sequence until water breaks through at a producer. Fracture propagation theory (Geertsma and de Klerk1) was applied to calculate incremental fracture length, or, the time interval during the fracture extension period. Combining the information of fracture extension frequency and incremental fracture length, expected breakthrough dates can be predicted at producers along the fracture azimuth. Water breakthrough sensitivity analysis is a useful technique to identify fracture azimuths or preferential permeability trends. Given daily surface injection pressure data, a simple method was developed to allow engineers to predict premature injection water breakthrough in tight reservoirs. This simple procedure is especially useful to reservoir and field engineers involved in secondary and tertiary recovery projects.