Jeetan Patel returned to the Black Caps in October in India, and by season's end was the side's premier test spinner.

Jeet Raval, Neil Broom and Colin de Grandhomme are expected to be the big winners when NZ Cricket names its 21 contracted players for the 2017-18 season.

The trio are expected to land contracts in place of fellow Black Caps Doug Bracewell, Mark Craig and Luke Ronchi.

Ronchi announced his retirement from international cricket on Thursday, followed soon after by Wellington team-mate Jeetan Patel who has enjoyed relative success with the Black Caps in a 2016-17 return to the team.

ANTHONY AU-YEUNG/GETTY IMAGES Wellington team-mates Luke Ronchi and Jeetan Patel are both retiring from the Black Caps after combining against South Africa last summer.

Contract awarding is a process led by coach and chief selector Mike Hesson who ranks his players on a set formula based on recent performance and likelihood of featuring in 2017-18. Tests carry double the weighting of ODIs and Twenty20 internationals.

READ MORE:

* Guptil to have a baby girl

* Afghanistan, Ireland granted test status

* Hopkins new ND T20 coach as CEO leaves

Raval, Broom and de Grandhomme were all in New Zealand's top XI at stages of the last home summer, and batsman George Worker looks to have grabbed No 21 for a second year running. Fast bowler Lockie Ferguson was probably next in line.

Craig's season was wiped out by injury, as was Bracewell's after he fell awkwardly on the slippery Yarrow Stadium turf and suffered a serious knee injury in December. Both will drop to domestic contracts, to be announced next month.

Retainers are understood to be a small increase on last season's which were $205,266 for No 1 - likely to be Kane Williamson for a third successive year - down to $83,498 for those ranked 18-21. Last season's match fees were $8495 per test, $3682 per ODI and $2407 per T20.

RONCHI, PATEL RETIRE

Asked about rumours he was calling time, Patel confirmed on Thursday from Chelmsford - where he took 4-138 and scored 71 for Warwickshire against Essex - that he'd played his last match for New Zealand at age 37. Like Ronchi, Patel will continue in Wellington colours this season.

Patel's international career looked over in 2014 when the offspinner turned down a West Indies tour spot to cement his hugely successful association with Warwickshire. It then roared back into life last October with a callup to India to replace the injured Craig, and by season's end he was New Zealand's leading test spinner against South Africa in Hamilton when rain denied him the chance to bowl his side to victory.

Patel's final international was the Black Caps' ODI defeat to Bangladesh in Dublin in May, ending a 24-test, 43-ODI career which began in August 2005. He was in the Champions Trophy squad but wasn't picked for any of New Zealand's three group matches.

Patel was keen to depart without fanfare when contacted, simply saying he'd enjoyed his comeback but it was time for him and NZC to move on.

Having left his mark on the South Africa series with white ball and red, Patel's absence will also provide a stern test of the country's spin stocks. Ish Sodhi is the likely beneficiary if he can prove his consistency at international level, with the jury still out on Mitchell Santner as a frontline test spinner.

Wicketkeeper Ronchi is understood to have told team-mates of his retirement decision during the home season. His last hurrah was at the Champions Trophy when elevated to pinch hitting opener; blasting 65 off 43 balls against Australia then scoring one against England and 16 against Bangladesh.

The Dannevirke-born 36-year-old played four tests and 85 ODIs; four of those for his adopted country Australia in 2008 before switching allegiance in 2013. His two highlights were a blazing 170 not out against Sri Lanka in a 2015 ODI, and 88 on test debut against England which helped New Zealand to victory at Headingley.

"It was a dream come true," Ronchi said of his career.

"I can't think of a better time to have been involved with New Zealand cricket. From the 2015 World Cup campaign, through to the overseas tours of that time and some amazing games and series, it's been a genuine highlight for me."

AT A GLANCE

Likely contract list (in potential ranking order): Kane Williamson, Trent Boult, Tim Southee, Ross Taylor, Martin Guptill, Tom Latham, Mitchell Santner, BJ Watling, Henry Nicholls, Corey Anderson, Neil Wagner, Jeet Raval, Adam Milne, Neil Broom, Jimmy Neesham, Colin de Grandhomme, Ish Sodhi, Matt Henry, Colin Munro, Mitchell McClenaghan, George Worker.