Beach blamed the deferral of gas and liquids production in the Cooper Basin for the cutback to between 8.1 million and 8.5 million barrels of oil equivalent (mboe) from 8.5 million to 9 million mboe previously.
Beach managing director Reg Nelson said while evaluations were still being carried out on the two exploration areas in the Cooper Basin where Chevron would take part, Beach had decided to go ahead with the investment deal.
"We've always recognised the need to have a big brother with the financial, technical and other capabilities in place," Mr Nelson told analysts on Tuesday.
"We thought we couldn't get a better partner than Chevron on this and offers like this are certainly things that you don't push off into the distant future," he said
"It will really add value in the very short term."
Under its agreement with Beach, Chevron will take an initial 30 per cent interest in one permit area in the South Australian sector of the Cooper Basin and an 18 per cent working interest in other area on the Queensland side.
The deal will provide Beach with up to $US349 million ($A340.27) million) over two stages, and exploration spending.
Beach on Tuesday reported net profit fell 22 per cent to $43.69 million for its first half to December 31, down from $56.06 million in the previous corresponding period.
However, underlying net profit was up 17 per cent to $60.9 million, with the difference accounted for by an unrealised loss on the revaluation of the company's convertible notes derivative.
"We have a strong underlying business," Beach chief financial officer Kathryn Presser told analysts.
Sales revenue was up 17 per cent to a record $344.7 million but costs roses also.
The company said record half year sales revenue was mainly due to a greater proportion of oil sales volumes.
Beach declared a fully franked interim dividend of 0.75 cents, unchanged from the prior period.
Beach shares on Tuesday were 0.5 cents higher at $1.37.