All-rounder Sciver picked up from where she had left off in the last game to score her third half-century of the tournament and help England Women post 143 for five on a tricky pitch.
In reply, West Indies struggled to get going with the bat and eventually folded for 97 at the Sydney Showground, which was largely thanks to the spin trio of Sophie Ecclestone (3/7), Sarah Glenn (2/16) and Mady Villiers (1/30).
England Women started afresh with Tammy Beaumont joining Danni Wyatt atop the order, but the move didn’t work as the new opener was trapped in front by Shakera Selman in the very first over.
Wyatt fell to a superb catch in the deep by Hayley Matthews off Anisa Mohammed’s bowling, but in Sciver and captain Heather Knight, England had the best duo to rebuild the innings.
Having scored more than 70 per cent of their team’s runs in the tournament, the importance of Knight and Sciver was not lost on anyone, with the latter reaching her third half-century in four games.
Amy Jones, in a new role at No.6, found back-to-back off-side boundaries off Stafanie Taylor but watched Sciver finally depart for 57 in the same over. Sciver’s knock took her tournament tally to 202 runs in four matches.
Just six balls remained as Brunt joined Jones in the middle, the bowler striking boundaries from the last two balls of the innings to take England Women to 143 for five.
West Indies also tinkered with their top-order as Deandra Dottin opened, but her innings ended on just nine with Ecclestone having her snaffled at short mid-wicket.
Taylor struck two boundaries off Brunt to end the Powerplay but that was to be her last significant contribution as he was stretchered off the field in the eighth over.
Star leg-spinner Glenn then got into her mojo, bowling out Hayley Matthews to leave West Indies two down in the ninth over.
It was to get even better for the spin unit as off-spinner Villiers bowled a wicket maiden after taking a smart return catch off Shemaine Campbelle.
Lee-Ann Kirby (20) did her best to inject some momentum with towering sixes off Glenn and Villiers, but Anya Shrubsole ended her exploits when the big-hitter was held by Sciver at long-on.
Ecclestone then had Britney Cooper stumped while Villiers effected back-to-back run-outs of Afy Fletcher and Aaliyah Alleyne.
Ecclestone then took her 100th international wicket by dismissing Anisa Mohammed to send England into the last four.
England Women: 143 for 5 in 20 overs (Nat Sciver 57, Danni Wyatt 29; Anisa Mohammed 1-23)
West Indies Women: 97 all out in 17.1 overs (Lee-Ann Kirby 20; Sophie Ecclestone 3-7, Sarah Glenn 2-16).