Abstract
This paper presents the results of propped fracturing operations conducted in the past 12 years in the Bach Ho (White Tiger) field offshore Vietnam. High temperatures (>275°F) and closure stress (>8,000 psi) combined with the fact that fracturing has to be performed from a vessel make the execution of fracturing treatments operationally difficult and challenging. More than 60 treatments have been performed in over 40 wells placing over 3 million lbm of proppant with a success rate greater than 85%. The wells targeted were both injector and producer wells. The post treatment results have been excellent with an average increase in Productivity Index (PI) of greater than 5 times.
This study discusses the properties of the various hydrocarbon-producing zones in the Bach Ho field. A general discussion of reservoir properties and damage mechanisms is included, which demonstrates the potential for stimulation and the associated benefits. The methodology adopted in the design, execution and evaluation of the fracturing treatments is discussed. Discussion on the rig-up of the fracturing vessel and the necessary modifications for efficient operation is also included.
A review of the treatments indicates that the majority of them are conducted at a flow-rate of 20–25 bbl/min (bpm), with a maximum proppant concentration in the range of 8–10 ppa (lbm of proppant added to 1 gal. of clean fluid) and proppant quantities of 60,000 to 80,000 lbm per treatment. High leak-off limits higher proppant concentrations and volumes. Higher rates are desirable but are limited due to limitation of equipment on the fracturing vessel.
Zones targeted are both the Oligocene (sandstone) and the naturally fractured Basement. Propped fracturing has been found to be very successful in the Oligocene whereas different types of treatments like propped fracturing, acid fracturing and acidizing have been tried in the Basement with limited success. Finally the lessons learned and the experiences gained in this field are shared.
