What Indy told about the plans of Germany for Stalingrad, the main goal was reaching the Volga and blocking all supply from the Soviet south towards the Caucasus region, so Germany can secure that region for themselves and rebuild the oil drills in somewhat peace there.
Because of the initial Soviet defeats in Fall Blau as a continuation of earlier Soviet defeats, surrendering more and mroe territory without any real resistance, I can see just pushing earlier for the Caucasus before cutting of the Soviets, getting to work earlier so to get the Oil without big resistance earlier, although this didn’t work out.
So the main goal became Stalingrad as a key city at the Volga to cut of Soviet supply towards the South. But as Indy explained City warfare is not suited for the Wehrmacht. So why didn’t the Wehrmacht go around Stalingrad in the North, push towards the river outside the City perimeters and then controlling the Volga there, to then also stop supply towards Stalingrad itself. Sure they can’t fully ignore the City itself, but it seems they don’t try to push around Stalingrad at all.
Currenty the Wehrmacht reached the outskirts of the city with a spearhead and then again spearheaded in the city in an even smaller area towards the Volga with very heavy fighting, instead of an (semi-)encircling siege attack.
This was answered in another post but in a nutshell it came down to logistics as the Volga is a wide river and would require transport across via barge and boat and then a secured beachhead. Then add to that you would need a steady stream of supplies and a solid road that could handle both weather and heavy traffic.
For the Germans it wasn’t practical and add to that the Russians would be able to see the buildup and they would be able to counter attack relatively easy.
For cutting supply, would they need to cross the Volga? Wouldn’t it be enough to build up a strong position at the Volga banks, north of Stalingrad to shoot all enemy barges that try to use the river to supply Stalingrad and the area south of it?
The main reason why the Germans can’t due an encirclement of Stalingrad is due to Hitler’s decision to divide Army Group South and Army Group A off in two different directions rather than follow the original plan to march both Army Groups to the Volga River to conquer the west bank of the River before turning Army Group A southwards to invade towards the Caucasus Mountains to secure the oil fields on the southern steppe. Even when the Germans reached the Volga, they lacked the strength to drive the Soviet forces back from the north and southeast of the city.
The Volga River is the equivalent of the Mississippi River in the United States or the Amazon River in Brazil. To the north of Stalingrad, the Volga River varies in width from 3 to 5 miles. The only way for the Germans to cross the Volga River would require the use of landing craft to conduct an amphibious assault across the river. From Stalingrad to Astrakhan, the terrain surrounding the Volga River is the equivalent of the bayou country of the lower Mississippi River. The Volga River is surrounded by swamps, oxbow lakes that used to be the Volga River, streams and rivers that used to be the Volga River in the past along with dry stream and river beds that flood after heavy thunderstorms. The terrain around the Volga from Stalingrad southwards only has a few roads that cross the bayou country. These roads can easily blocked and most of the terrain becomes swampland after a series of heavy thunderstorms. So all of the dark green that you see on the aerial image is bayou country. This is the reason why the Germans can’t encircle Stalingrad. The city of Stalingrad is actually built on bluffs and cliffs overlooking the Volga River so it has the best terrain in the area for using Artillery to interdict the river.