Laboratory and Field Evaluation of the Role of Drill Solids in Formation Damage and Reduced Horizontal Well Productivity

Abstract

This paper examines the role of drill solids in causing formation and completion damage in horizontal openhole completions. Drill solids are routinely kept to a minimum in drilling fluids, mainly to improve drilling properties. However, these drill solids, even at low concentrations, represent a significant source of insoluble particulates that become incorporated in the drill-in fluid filtercake. Not only is the potential for formation damage greater, but these filtercakes laden with insoluble drill solids can be deposited on screens resulting in reduced productivity through screen plugging. The objective of this paper is to illustrate the effect of drill solids contained in drill-in fluids on formation damage and well screen plugging and to emphasize the importance of minimizing solids, not only to maintain the desired drill fluid rheology, but also to effect better filtercake cleanup. New laboratory test methods have been used to study formation damage in a 2-foot long horizontal wellbore model incorporating dynamic filtercake deposition on natural and synthetic core material. The model measures formation damage in radial flow. Formation damage tests with drill solids were performed for both water based and synthetic based drill-in fluids. Testing was also performed to simulate prepacked screen damage using a variety of commercially available drill-in fluids and common resin-coated gravel sizes. Results of these tests with laboratory-prepared fluids have been compared against the performance of field fluids and will eventually be correlated with field well performance. Background The use of horizontal wells to maximize recovery of oil and gas has become commonplace. However, operators frequently find horizontal wells do not provide the expected productivity after completion. While cased hole completions exploit perforation techniques to bypass the zone of formation damage caused by drilling, the openhole completions commonly used in horizontal wells do not provide a means of bypassing this damage. Previous work has discussed formation damage caused by drill-in fluids. Often, these studies have concluded that formation damage is caused by solids invasion into the rock or from damage caused by incompatible fluid filtrate. Some investigators have presented evidence that DIF filtercakes did not penetrate into rock matrices. Fraser's study showed ESEM photo images of different types of DIF filtercakes tightly compacted onto formation rock surfaces. He found very little filtercake invasion in the rock matrix. Burnham and Browne have discussed the concept of "lift off" pressure that can be used characterize the behavior of DIF filtercake on formation rock. Their studies suggest that "formation damage" can be caused by too "tight" a filtercake on rock surface. P. 749

Return Permeability: When A Single Number Can Lead You Astray In Fluid Selection

“…The above method provides a means to assess the relative damage mechanisms associated with the selected RDF. However, if a sand-control screen and/or gravel are introduced, additional assessment/techniques are required to determine compatibility or damage as introduced by the residual filter cake deposited from an RDF system (Hodge 1997;Burnett et al 1996;Price-Smith et al 1998;Burton et al 1998). In this scenario, a base line test may be required that includes a screen coupon, gravel or both.…”

Mud-Induced Formation Damage in Carbonate Reservoirs: Consequences on Productivity of Open-Hole Horizontal Wells

“…It includes measurement of Flow Initiation Pressure (FIP) for cake lift-off and removal of external filter cake damage. FIP is controlled by the cake property, but also the formation permeability and internal damage [6][7][8][9][10] . Removal of filter cake is done either by natural cleaning with the formation drawdown pressure or by chemical treatments with conventional acids and oxidizers or more sophisticated products like enzymes [11][12][13][14][15][16] .…”

Field Test of a Novel Drill-In Fluid Clean-Up Technique

“…Tests conducted in Joint Industry studies (CEA 73 etc) and in Conoco internal testing have shown that screen permeabilities can be reduced from hundreds of thousands of milliDarcies initially to less than 10 mD due to filter cake plugging. [1][2][3][4][5] In cases where formation collapse occurs, the filtercake material mixes with the formation sand and reduces hole/screen annular permeabilities to values that can be significantly less than reservoir permeability. For this reason, many operators perform acid washes to remove filtercake prior to flowing the well.…”

“…These acid washes can effectively remove filtercake, however they can also lead to corrosion problems if the acid cannot be effectively inhibited for the required acid/screen contact time. [2][3][4][5][6] Corrosion control is especially difficult in production wells subject to long shut-in periods prior to flow back. In a number of cases, concerns about screen corrosion have led to elimination of the acid wash stage and attendant poor well productivity.…”