This does not appear to be true. There's no mention of it in Weinberg's A World at Arms, which is about the best one-volume history of WWII. The German multi-volume history Germany and the Second World War covers this period in volume 2, Germany's Initial Conquests in Europe, pages 118-126. Warlimont's memoirs, Inside Hitler's Headquarters 1939-45, have further details. While Warlimont is often self-serving, he doesn't portray himself in a good light here, and so his account is worth considering.
The German High Command, OKW, did not expect the Soviet invasion of eastern Poland at the time it happened, according to Warlimont. It came as a surprise to them, and they did not know about the treaty of 23rd August, or the agreed boundary. Orders were got out as fast as possible (which wasn't very quickly) since the potential for clashes was obvious. The Soviet Military Attaché in Berlin was briefed by Warlimont on 17th September on the progress of the German invasion. Since Warlimont hadn't been told about the boundary by then, he stressed the German claim to the oil area in that briefing and thought he was going to be fired once Stalin telephoned Ribbentrop to complain.
Should OKW have anticipated the Soviet invasion? The Poles had defeated the proto-USSR in 1919-21, the Soviets seemed to be pre-occupied with their conflict with Japan, and the Germans had a low opinion of Soviet capabilities in general. The Germans advanced beyond the agreed boundary line because the Wehrmacht didn't know about it. Even if they had known, they would likely have crossed it so as to be able to defeat the Poles, rather than giving them a safe area to rally in.
Once the Soviets attacked, OKW laid down a maximum limit to the German advance on 17th September and required units beyond that line to pull back. Subsequent lines were laid down every day from 18th to 21st September, pulling German forces back to the "four rivers" boundary line that had been agreed on 23rd August, backed up by orders from Hitler. The intention was to keep German and Soviet troops apart, and to give the Germans time to move back wounded, prisoners, and their own and captured material. Another reason for doing it in stages was to avoid giving various undefeated Polish forces time and space to regroup.
The Germans hoped to revise the agreed boundary, and there were various changes, but the Polish oil fields had always been on the Soviet side of the line, and stayed there. There was no fighting involved in the Red Army taking them over, according to all of these sources. The withdrawal from Brest-Litovsk was amicably negotiated by German and Soviet commanders on the scene, and there was a joint parade before the Germans left.