Hydrocarbon production can be hindered as a result of fluid-induced formation damage caused by shale damage (swelling, sloughing, or fines migrating) or chemical damage (insoluble residue or polymer buildup). The proper selection of completion and stimulation fluid with additives provides the leading approach to mitigate formation damage.
Formation-specific damage mechanisms were determined from formation core, drilled cuttings, and outcrop materials for more than 100 North American resource shale samples. The formation materials were characterized using x-ray diffraction (XRD), cation exchange capacity (CEC), swelling sensitivity time (SST), mechanical stability turbidity (MST), and column flow testing to determine mineralogy, fluid sensitivity, and dominate fluid-induced damage mechanism. Preventing formation damage is predominately achieved with cationic clay stabilization chemicals. The efficacy of numerous chemical additives prepared at the same activity but with varied molecular weights (MWs) from 0.1 to 1,200 kDa was evaluated on ultra-low permeability shale samples based on reducing the swelling, fines generation, and mechanical destabilization tendencies. The same treatment chemicals were evaluated for permanency, compatibility with anionic friction reducer (FR) polymers, and mobility within porous media to determine the ideal North American formation stabilization material.
Fines generation was determined to be the dominant fluid-induced damage mechanism for ultra-low permeability North American hydrocarbon-producing formations. Clay content for these active formations range from 1 to 70 wt%, with an average of 30 wt% and a CEC of 4.5 milli-equivalence (meq)/100 g, indicating that most North American formations have moderate fluid instability. Fluid sensitives found an average swelling damage comparable to a 1 wt% smectite sample (30 seconds) mass loss due to mild mechanical agitation similar to an illite sample (3.2 wt%/hr) and fines generation due to flow approximately half of an illite sample (6.22 mg/PV). Prevention of these fluid-induced formation damage effects was determined for cationic clay stabilization chemicals ranging in MWs from monovalent salt solutions to large polymeric materials. Highly mobile monovalent salts effectively prevent swelling and remain compatible in an anionic FR solution; however, these treatments are temporary and less effective for remediating fines generation. Increasing the MW of cationic treatments improves the performance in terms of preventing swelling, fines, and wash-off; however, if the MW increase is too large, the polymers reduce permeability and become incompatible with anionic FR polymers. There is a range of moderate MW materials that provides permanent protection against swelling and fines damage while remaining compatible with anionic FRs. This range of moderate MW cationic treatments is the optimal chemical additive for most North American formations, offering the most effective protection against prevalent fluid-induced formation damage mechanisms while preventing chemical damage.