document

Abstract

Increasingly, operators are looking for simple and effective methods to overcome the hazards and limitations imposed by depleted reservoirs, rubble zones or thief zones. One method is to utilize casing or liner drilling to isolate the problem area by combining drilling and casing in one operation. This can take on many forms from simple drill-in systems to full retrievable directional BHA’s connected below the casing or liner string. 

A major independent operator has recently drilled two 12-1/4” hole sections in different wells to isolate a problem thief zone (Well A-2 BP01 and A-3). The drilling of one of these sections with liner (A-2 BP01)[1] and the other with casing (A-3) produced many operational and equipment learning that will increase efficiency in future applications. To drill the problem interval of the A3 well, the operator chose a tried and proven Casing Drive System, together with a new PDC casing bit2 to drill down a full string of 9-5/8” casing.

The choice of drilling with liner or casing is examined along with the equipment and operational practices required. Comparisons will be drawn with the offset well which was drilled conventionally and led to mud losses of over 3,000 barrels, the effectiveness of a smear or plastering effect while drilling with liner and casing is investigated. 

Introduction The Eugene Island 364 field in the Gulf of Mexico is an area of rapidly deposited young and undercompacted sediments. In areas such as this, standard drilling engineering fundamentals such as fracture gradients, pore pressures and rock properties can be unpredictable[1]. 

The 12-1/4” hole section of the subject well A3 was drilled with casing following the drilling of A-2 BP01 with a liner and A-2 and A-1 conventionally. The A-1 well had experienced numerous geological, mechanical, and wellbore stability issues. 

The well design for well A-2 and A-3 were developed based on lessons learned in A-1. Specifically, severe mud losses in the TB-4 sand were recorded in A-1, using oil-based mud (OBM). An overbalanced hydrostatic mud weight was determined to be the cause of the losses. 

A-2 and A-3 utilized a water-based mud (WBM) system and casing set below the TB-4 sand to isolate the thief zone encountered in A-1 and prevent lost circulation (Fig 1). A 13.6-ppg WBM was used to drill A-2 through the TB-4, but the well still experienced severe mud losses. The operator chose to plug back the well and bypass the original wellbore rather than fight the severe losses and instability. A-2 BP01 was successfully drilled with a liner for 269 ft @ 7.4 ft/hr through the TB-4[1]. 

To drill the problem interval of the A-3 well, the operator selected a service company with a proven Casing Drive System and expertise together with a new PDC casing bit to drill down a full string of 9-5/8” casing.