Robert C. Burton

The Impact of Formation Damage and Completion Impairment on Horizontal Well Productivity

Many horizontal wells in unconsolidated to weakly consolidated formations are completed open hole with sand-control screens to prevent production of formation sand. In these completions, the screens are designed to retain formation sand by incorporating outer layers of resin-coated gravel, porous metal sheets, or tightly woven wire mesh. These screens are prone to plugging with mud and drill solids. In weaker zones, the formation may collapse onto the sand-control screen.

A Multidisciplined Approach to Designing Targets for Horizontal Wells

A multidisciplined approach to developing 3D target diagrams and their associated tolerances provides a cost-effective method for designing horizontal wells. The key to this approach is that the diagram quantifies and communicates the uncertainty of the target boundary conditions to others involved in designing and drilling a well. Field examples show how a multidisciplined team creates a 3D target diagram. The preliminary 3D diagram is used to examine the combined uncertainty in the position of the features constraining the target. To maximize the target size, the team must decide on the relative importance of each constraining feature and assign target tolerance limits. The final target diagram minimizes both risk and cost to produce the optimum well design.

Evaluation and Selection of Drill-In-Fluid Candidates To Minimize Formation Damage

Conoco drilled and completed a horizontal well in a depleted, high-permeability, oil reservoir. The formation is an unconsolidated, clean sandstone with absolute permeability over 3300 md. The unconsolidated nature of the formation combined with its low pressure and high permeability caused concerns regarding hole stability, fracturing, excessive fluid loss, and differential sticking. To identify the best drill-in fluid for the horizontal section, the evaluation of fluid candidates focused on both drilling properties and formation/completion damage potential. The testing compared fluid performance in standard API drilling fluid tests, low-shear rheology at elevated temperature, dynamic fluid-loss behavior at elevated temperature, and core flow tests. The flow testing was performed with cores from an offset well to simulate damage due to drill-in fluid exposure and evaluate remedial treatment options. Also, a new lab-scale procedure was developed to observe the tendency of pre-packed screens to be plugged by drill-in fluid filter cake and unconsolidated formation sand. In addition to the laboratory testing, a review of the drilling and completion operations is presented, including performance of the drilling fluid at high overbalance pressure (∼ 2600 psi) and the design and execution of subsequent remedial treatments. The production history is discussed and related to laboratory observations regarding cleanup and remedial treatment effectiveness.

Results From the Heidrun Field Cased-Hole Gravel Packs

During the initial phase of the Heidrun field development, five wells were precompleted with state-of-the-art cased-hole gravel-packing techniques. The wells were tested and temporarily abandoned, awaiting tieback to the Heidrun tension-leg platform (TLP). This paper describes the completion techniques applied and presents results of an evaluation of gravel-pack efficiency for the wells. Flow and buildup tests were carried out on the semisubmersible drilling rig before and after gravel packing to evaluate initial productivity. Stabilized well-test data acquired on the Heidrun TLP at full production are presented to document ultimate completion performance for each well.

Evaluating Completion Damage in High Rate, Gravel Packed Wells

Conoco has completed and tested a series of high rate, gravel-packed oil wells. Analysis of the well test data for the first completion indicated significant formation/completion damage had been caused during the gravel-packing process. Extensive laboratory testing designed to closely simulate the completion procedure was performed in conjunction with detailed completion pressure loss evaluation. The studies identified the LCM pill used during completion operations as the primary source of damage. A new, self-breaking, LCM composition was designed that provided fluid-loss control with minimum formation/completion damage. This LCM system and a number of other design improvements were then used in the fields remaining gravel-packed completions. This paper describes the analysis of well test data and the application of this information to evaluate completion procedures for these high rate, cased-hole, gravel-packed completions. The analysis technique used is unique in that it uses a combination of laboratory, analytical, and operational data to quantify individual components of the total measured pressure drop across the completion. This approach provides a significantly better insight into completion performance than merely stating an overall completion pressure drop, skin value, or well flow efficiency. This systematic analysis of pressure losses resulted in a better understanding of formation damage effects and the factors that influenced them during the completion process. This in turn allowed completion procedures to be modified to target specific areas for improvement.

Waste Water Recycling in Steamflood Operations

A pilot waste water recycling project was conducted at Conocos Cat Canyon Field, Santa Barbara County, California. The project developed a process to treat the fields high silica produced water for reuse in steam generation. The treatment of produced water was found to be more complex than conventional fresh water treatment techniques currently employed in the field. Oil, solids, and iron were each removed from the process stream before softening the water. Softening was then conducted in a two-stage process consisting of strong acid primary softeners followed by a weak acid polisher. Continuous operation of this pilot recycling plant virtually eliminated scale deposition inside a test steam generator.