Novel Drilling, Completion and Workover Fluids for Depleted Zones: Avoiding Losses, Formation Damage and Stuck Pipe
- P. Reid (Impact Solutions Group) | H. Santos (Impact Solutions Group)
- Document ID
- Society of Petroleum Engineers
- SPE/IADC Middle East Drilling Technology Conference and Exhibition, 20-22 October, Abu Dhabi, United Arab Emirates
- Publication Date
- Document Type
- Conference Paper
- 2003. SPE/IADC Middle East Drilling Technology Conference & Exhibition
- 4.3.4 Scale, 5.5.2 Core Analysis, 2.4.3 Sand/Solids Control, 1.8 Formation Damage, 1.11 Drilling Fluids and Materials, 5.1 Reservoir Characterisation, 3.2.3 Hydraulic Fracturing Design, Implementation and Optimisation, 3 Production and Well Operations, 1.6 Drilling Operations, 1.6.1 Drilling Operation Management, 1.6.9 Coring, Fishing, 4.1.2 Separation and Treating, 1.7.1 Underbalanced Drilling, 5.8.7 Carbonate Reservoir, 5.2 Reservoir Fluid Dynamics, 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc), 1.11.2 Drilling Fluid Selection and Formulation (Chemistry, Properties)
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As oil and gas fields become mature, there is an increasing need to drill, complete and workover wells in depleted zones. The proximity of normally pressured zones often means that, in order to maintain wellbore stability, the depleted formations experience very high overbalance pressures - often exceeding 1000psi. As a consequence, problems such as differential sticking, deep filtrate invasion and severe lost circulation are common. In the extreme, increased costs and high levels of formation damage can make continued exploitation of fields uneconomic.
This paper describes a new fluid additive package designed to form an effective, low permeability barrier on permeable formations. The materials have been used in a wide range of water, oil and synthetic based fluids with excellent results. We present laboratory evidence and field data to show that fluid invasion is greatly reduced. This brings several important benefits:
Differential sticking is greatly reduced
Fracture gradients are increased (increases well over 1000psi have been observed).
Return permeability results, and hence well productivity indications, have been excellent.
The paper discusses the mechanism by which the additives provide superior invasion control, and the ease with which the protective barrier is removed from producing intervals.
The materials have been used onshore and offshore in most major oil and gas provinces. In addition to providing effective technical solutions, they have the environmental approvals that allow their unrestricted use in areas such as the Gulf of Mexico and the UK North Sea.
Depleted zones are becoming more and more common as many fields become mature. Drilling activity in old fields can be significant, either in trying to maintain the production level, or in trying to reach untapped hydrocarbon pools. Workover activity is also generally high.
The challenge of working in depleted areas increases when zones with normal or original pressures coexist with the depleted ones. Several problems can be faced during drilling, completion or workover that were not present when the fields were first developed. These changes often require modified procedures and techniques if the fields are to be developed economically. In some situations, fields will have to be abandoned if this economic development cannot be realised.
One of the techniques developed to combat the difficulties of operating in depleted zones is Under-balanced Drilling - UBD. There are several publications describing this technique in detail1-3. However, there are technical limitations that mean that UBD cannot be used in many cases. In these situations, a more traditional drilling operation must be used.
This paper focuses on those cases where a drilling fluid with an overbalanced pressure must be used. The paper initially describes the traditional approaches used in formulating drilling, completion and workover fluids for depleted zones, emphasizing the benefits and limitations associated with each of them. We also discuss recent technology introductions, focusing on aerated fluids and, more importantly, on a novel family of ultra-low invasion fluids. These new fluids are discussed in detail, including their mechanisms of action and why they are suited to depleted zone drilling. Laboratory results and field cases are used to demonstrate the utility of these new fluids in developing depleted reservoirs economically.
The Traditional Approach: Particle Bridging
For a long time the industry has known that minimizing invasion of wellbore fluid into the rock is a key part of the strategy for dealing with depleted formations effectively. An established approach is to add particles to the fluid to bridge the pore throats. If the formation pore sizes are known, these particles can be sized in such a way as to provide effective cake building properties. Calcium carbonate and salt (sodium chloride) are the most commonly used particles, because it is reasoned that acidification or simple dissolution can remove these solids from inside the rocks pores, should stimulation be necessary.
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